When comparing Solar 2D (formerly Corona SDK) vs PlayCanvas, the Slant community recommends Solar 2D (formerly Corona SDK) for most people. In the question“What are the best 2D game engines?” Solar 2D (formerly Corona SDK) is ranked 15th while PlayCanvas is ranked 65th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Very simple to use

Pro Free
Corona SDK is completely free. That includes pro-tier plugins.
Pro Corona Simulator
Corona SDK ships with Corona Simulator, which runs your game/app directly on your PC/Mac and updates every time you make changes.
It provides immediate feedback to your actions, you can see your changes right on the screen, without necessity to make build to device. Getting instant feedback really boosts tenfold prototyping and development speed.

Pro Good documentation and lots of tutorials
Pro Content scaling
It's easy to create a game that looks good on many different sized mobile devices.
Pro Live builds - update builds running on a device automatically
With the live build feature, once you have created a build and installed on a device, you get lightning fast turnaround times because any change on the code or data is updated to the devices running the game (within the local WiFi) immediately. So changes can be tested on the real hardware within a very few seconds.
What's even more impressive, this even works flawless with multiple devices running the game. You have to use it to learn how good of a feature this is while development and even more, while doing QA. Imagine fixing bugs and everyone of your QA team/friends/whoever helps to get your game done, has all changes on his device without doing anything but waiting 5 seconds - outstanding.
Pro Lua syntax
Uses the great and easy-to-learn Lua programming language.
Pro Very comprehensive API
It's very quick to get things up and running with Corona SDK. The API is extensive and while it's not 100% feature-complete with the iOS API, it's close enough that you could create tons of games and never run into a roadblock.
The API docs can be found here.
Pro Amazing learning curve
Corona does not throw photoshop-like madness full of buttons editor. You can go as fast as you want, learning and building game from ground up. Eventually, you'll learn how much corona is doing for you. But to start you don't have to master complex editor software. It's a great tool to learn to start game development if you want to learn how to program and make games. Your experience will be 100% transferable to any other Pro game engine.

Pro Cross-platform desktop and mobile
Corona works on OS X, Windows and Android (including Kindle Fire & Nook).
Pro Marketplace for 3rd party plug-ins

Pro Great community

Pro Ability to call any native (C/C++/Obj-C/Java) library
Pro Completely free
Since Corona SDK became Solar2D, it's completely free, as only some third-party plugins are paid.
Pro Open Source
Since Corona SDK became Solar2D, it's completely open source under MIT license.

Pro Well supported
Pro Real-time collaborative online editor tool
PlayCanvas has an online editor that lets you build scenes and work with other people in your team in real-time. This is all done through the web browser without having to install any additional software.
Pro Powerful assets pipeline
Assets and content delivery is very different on a web platform comparing to native. So PlayCanvas challenges best practices to allow developers decide how their content is delivered and in what form.
Async Assets download allows developers to load content as the app goes, instead of asking to download all assets in advance risking users to simply navigate away while staring at loading screens.
Formats for 3D models and textures support covers all the popular tools. And the workflow is as simple as dragging and dropping your files right into the Assets Panel. The cloud will do the rest of the hard work optimizing and converting your files into runtime-friendly and compressed data.
Pro Rendering engine runs on the browser
Has an advanced WebGL renderer that runs in the browser.
Pro Avoids having to download lots of textures for lightmaps
Lightmaps are an efficient way to deliver lighting to your scenes for a long time. But they come with the cost of large textures. PlayCanvas offers a unique solution for a web platform, it renders lightmaps when an app is loading in runtime.
This is faster than downloading MBs of textures. And it's much more convenient: simply switch your light sources to bake, and static models to be lightmapped, and the engine will do the rest.
Pro Friendly and active community
PlayCanvas has Feed as homepage for registered users, listing Dev Logs of other developers. This allows to socialize with other developers like yourself in a twitter-like environment.
More to that, there is also an active forum, where developers help each other to solve their challenges.
Developers of PlayCanvas itself are always looking forward to chat and help the community with any problems that may arise.
Pro Integrated physics engine
PlayCanvas lets users integrate physics in their game rather easily, using the powerful Bullet Physics Engine (ammo.js). Should also be noted that the physics engine is delivered as an optional library, so by default being disabled it does not add any extra download size to your apps.
Pro Has a free tier
Engine is free for projects under 200MB and with no more than 2 people on a team. The free tier has no engine restrictions.
Tools are totally free too. There are no special limiting features behind any paywalls, and free users have all the features as paid users.
There are no royalties associated with publishing your apps and games - you've made them, you own them.
It is free to publish to playcanvas.com as well, just by one click in Editor.
Pro Cross-platform support
PlayCanvas lets you build games that run in mobile, desktop browsers, and native mobile apps. PlayCanvas can even make games that can run inside mobile social media and instant messenger clients like Twitter and WhatsApp.
Pro Small app size
The engine itself weighs just under 150Kb, and it's always challenged to stay small. There is no extra weight that has to be carried with your app, just your assets and scripts in a runtime-friendly compressed form.
This allows users to engage with your content in matter of seconds, and even just under a second on a good connection.
Pro Open source
PlayCanvas is fully open source and is under active development.
Pro Very easy to use
Pro Loads extremely fast
Pro Has hot code reloading
Real-time link between your launched app and the editor allows the developer to preview and play with their scene without needing to refresh the game after every change in the code to see the updated result.
Cons
Con Free, but not completely
Con Making a device build requires internet connection
To build your app for the device (iOS/Android/AppleTV) Corona requires to fetch resources from online. This would include base application template and plugins. This allows not to perform local build or use Xcode or Android Studio to do a build. Even Large games/apps would build very fast with good internet connection.
Your code never leaves computed. Corona SDK would transfer some information to determine which plugins and pieces has to be transferred in order to make a final steps in build.
As a bonus - you get basically one button press to get from your Corona Simulator game to game on a device.
Con Private projects are only available for premium users
The free tier does not support any private projects. Instead, all the code and assets will be hosted openly. While not a problem for open source games and for developers who intend to make an open source game, it can be a deal-breaker for teams who want to keep their code and assets private.
Con No collision offset
Con Not many tutorials
