When comparing GameMaker: Studio vs Modd.io, the Slant community recommends GameMaker: Studio for most people. In the question“What are the best 2D game engines?” GameMaker: Studio is ranked 6th while Modd.io is ranked 94th. The most important reason people chose GameMaker: Studio is:
Game Maker Language (GML) is the primary scripting language that is interpreted similarly to Java's Just-In-Time compilation used in GameMaker. It is used to further enhance and control the design of a game through more conventional programming, as opposed to the drag and drop system.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Gives developers access to a more fine-grained controle over the logic through the Game Maker Language
Game Maker Language (GML) is the primary scripting language that is interpreted similarly to Java's Just-In-Time compilation used in GameMaker. It is used to further enhance and control the design of a game through more conventional programming, as opposed to the drag and drop system.
Pro Extremely easy to learn
GameMaker: Studio is incredibly easy to learn. It requires almost no programming knowledge which means that those without the technical experience, such as designers or artists, can create their projects without the help of a programmer.
Pro Easy to find resources/tutorials/assistance
GameMaker: Studio has a huge following, tons of people put up tutorial videos, and it's just generally easy to find help. It has a huge community.

Pro Easy cross-platform shader support
Write your own shaders in one shader language and have it automatically ported to all platforms. You can even choose a specific shader language to wield the full power of the target device.
Pro Assets can easily be found in the official marketplace
Yoyogames website has a marketplace which opens up an opportunity for people to sell or giveaway created assets and resources (sprites, scripts, sounds, extensions, full source codes, etc.) for use in GameMaker. This benefits people who needs quality assets for their games, and for creative people to provide these assets for extra income. The Marketplace has a rating system so it can eventually increase the quality and competitiveness of the assets submitted.
Pro It has an IDE used for loading all of the assets
It is very easy to manage all the resources you want to put in your game, the UI widgets for each assets (sprites, sounds, backgrounds, rooms, objects and shaders) are intuitive enough for when adding or even editing the properties of each your assets. The included editors are also good and easy to use (sprite/image editors, shader editor and room editor).
Pro Extremely stable
GameMaker: Studio has been around since 1999 and has been used and maintained during all this time. This makes it an extremely stable game engine.

Pro Cross-platform multiplayer support
There is the possibility of creating games that interact with different platforms and is not that hard.
Pro Built-in support for pixel-perfect collisions
Enabling pixel-perfect collisions on 2D sprites is so easy many will likely turn it on when maybe they might be better off without it. Regardless, it simplifies small and/or retro console-like game work. This is a feature fairly unique in this class of game engines.
Pro Cross-platform
GameMaker: Studio projects can be deployed to: HTML5, Linux, Windows, OS X, Windows Phone, Android, iOS and PS3/4/Vita.
Pro Easy to use
Game Maker Studios simple interface allows for rapid prototyping, and easy development.

Pro Supports 3D
There is also 3D support that doesn't interfere with the primary 2D focus.
Pro Easy to add native code to GMS
Good extension support. You can do anything with gms! You just need to know how to code natively in the respectively export (like Android).
Pro Its Fun, its easy to script
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Pro Runs well on low-end devices
The game client doesn't use much CPU nor bandwidth.
Pro Free
By far, this engine is completely free to use.
Pro No installation required - super easy to get started
Modd.io runs in browser, it provides IDE, map editor, and asset manager all in one platform, so you don't need to download or setup anything.
Pro Easy to use free Asset Library
You can easily change your game assets (images, sound, etc) with a single click using modd.io Asset Library
Pro Has multiplayer support baked in
This engine supports up to 64 concurrent players, and hosts servers for you as well
Pro Perfect for Impatient game developers
It literally takes 5 minutes from signup to publishing my game
Pro Easy to use
Modd.io is designed for new/intermediate developers who wants to get into game development. You should be comfortable using the engine after spending about 15 minutes in watching tutorial videos
Cons
Con The scripting language used is quite limited
Language does not support actual objects, structs, real data types, functions, overloading, even argument naming. Developers generally have to code around the lack of these features in very tricky ways.
Con No GUI editor
The GUI must be hard-coded, leaving a lot of tricky calculations and jumping through hoops to accommodate different devices and displays; it's probably the least developed and hardest thing about GMS2 compared to comparable engines

Con Destructive DRM
In late 2012/early 2013, YoYo Games released a version of their new Studio IDE for cross-platform development that would import games and destroy all of the image type resources for some legitimate purchasers of the software by superimposing a pirate symbol on top of the image. This was due to a fault in their digital rights management software implementation which they use as a method of combating pirated copies of the software. Though the false positives bug is reported to be fixed, the DRM is still in place and may affect placeholder graphics, etc. YoYoGames publicly stated they would remove the DRM at a later point in time, but that other less-invasive DRM techniques would remain.
Con Exporting to some formats costs extra
You need to buy extra modules to be able to export to platforms like Android, iOS, HTML5 and others.
Con No built-in refactoring tools
There are no built-in refactoring tools. For example, you can rename a resource, but GM:S will not automatically change the mentions of it across the code to the new name. Furthermore, because all file formats are text-based, basic refactoring could be achieved by simply doing "find & replace in all files" -- which is a feature offered by pretty much every external code editor nowadays -- but no such feature here. Hitting Ctrl-F will pull up a rather odd Find/Replace box but selecting a word before hitting Ctrl-F will not autofill the Find field for you like it will in most tools. Even that you have to cut and paste yourself.
Con The cost to buy for development is outrageous
The cost for this tool is hindering for indie developers who have little money to work with.
Con Bad history of ignoring critical bugs
In the past, the developer failed to update the software for iOS and Android when game-breaking updates were made to those platforms.
Con Development has been and will be cosmetic
The change from 1.x to 2.x was cosmetic, the engine and language stayed the same. The roadmap for future development is also cosmetic and includes updating the sprite editor, adding an audio editor, and adding a "mini map" for the IDE.

Con Poor level editor
No marquee select, no layers, can be glitchy, no grouping, etc.
Con Can't embed videos in game
Doesn't support embedding videos in a game.
Con Expensive for what it offers
There are several options with more flexibility, better learning resources, and a lower price point.
Con Proprietary language forces expensive "lock in"
Because it uses GML, a very non-standard custom language, new users do not learn a transferrable language and become locked in.
Con Tends to crash or not compile games properly
Con Poor accessibility and integration
Documentation and resources largely focus on proprietary scripting language, which is necessary for achieving full potential of the software due to poor drag and drop integration.
Con No way to activate or use existing modules
Support entirely focused on new iteration depriving even basic functionality of this version with any purchase that hasn't already been activated. It is still possible, thought not intuitive, to download this version on the trail screen for GM S 2. But no purchased (wildly expensive) module can be added any longer.
Con Code editor not friendly to indented code
While the editor of course has features for intending code such as auto indent and smart tabs that can be turned on or off, these features work in unusual ways and, overall, the editor is not very adaptable to various typing styles. Also, Home always takes you to position 0 and never to the beginning of the text no matter how many times you hit it. Thus, if you hit Home and then Enter a new line, with auto indent on, it will always mess up the indentation on the line following the new line leaving you to fudge around to fix it manually. If you prefer tabs over spaces, forget it. Finally, if you leave the GameMaker app and try to click back into the code editor, the code editor will not fully get the focus sometimes leaving you with the ability to type but not tab. It usually takes two clicks to fully focus the code editor from outside the GM app.
Con This is very flat for games
They are not beautiful - for example, Undertale.
Con Owned by a gambling company, Playtech
As opposed to other engines, which are open source or owned by game companies, GameMaker is developed by YoYoGames, which is owned by Playtech, a gambling software company.
Con The engine is evolving in a bad way
Over the last updates, many useful features have been removed, making it harder to create more complex games.
Con Not very secure
Modd.io comes with its own security issues. Many of them have been used to destroy eachother's games, which completely busts your progress on your game unless you have backed it up by exporting it's JSON.
Con Not Possible for stuff
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Con Annoying asset size limit
Each asset is limited to 800kb (except for audio being 3mb) which is okay for simple assets but unacceptable for creating spritesheets for animations or tilesheets for the map.
Con Very flat map
No matter how well game maps are made, all of them look just not beautiful.
Con No/limited camera manipulation
You cannot create a shake effect which is also urgently needed in complex game creation.
Con Certain variable datatypes are urgently needed but do not exist.
Such datatypes as arrays composed of numbers, strings, etc are needed to create complex games but just do not exist in this game engine.
Con Joke-y community
Most of the staff team in the community are constantly behaving like jokers. It just always feels like 80% of the staff team is not the right pick for such a community.
Con The homepage is not good
The homepage allows players to join your game, but the way it works is just not good. The "unpopular 0 player" games get less exposure than the popular games. The tier system also puts a star on your game card which also lures players to your game making them think this game has a special event or something, giving a disadvantage to the less popular games which are still so called "Tier 1".
Con Not very powerful
This engine is ready to use right away, but already starts dropping framerate at over 1000 units which are not very active.
Con Tier-based servers with certain lockdowns
Modd.io "tiers" all the games you create. The very basic tier, commonly called "Tier 1" is very limited and removes motivation to develop a game.
Con You'll have to learn a new programming language
This engine has it's own IDE with a drag and drop style programming language. It does take a good 2 hours to get familiar with the API..
Con No lower level API access
You cannot access lower-level APIs through this engine, such as the renderer.
Con No single player support
All games in modd.io must support multi-player game mode.
Con Limited customizability
Modd.io is designed to be good at making "specific" kind of multiplayer games. Its strength unleashes if you don't care too much about the specifics in UI. For example, if you wanted to make a casual death match game, it is extremely easy to make it using modd.io. However, if you want to create a puzzle game with a unique UI, it becomes very time consuming.
Con No 3D support
This engine is limited to 2D only.
