When comparing Unreal Engine 4 vs Skyline, the Slant community recommends Unreal Engine 4 for most people. In the question“What are the best 3D game engines?” Unreal Engine 4 is ranked 2nd while Skyline is ranked 39th. The most important reason people chose Unreal Engine 4 is:
Blueprints are authoring tools designed for non programmers so designers and other team members can help tweak and prototype. UE4's Blueprint scripts resemble flowcharts where each box represents a function or value, with connections between them representing program flow. This provides a better at-a-glance indication of game logic than a simple list of events, and makes complex behaviors easier to accomplish and games a lot faster to prototype.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro A visual scripting system for non-coders enables quick prototyping
Blueprints are authoring tools designed for non programmers so designers and other team members can help tweak and prototype. UE4's Blueprint scripts resemble flowcharts where each box represents a function or value, with connections between them representing program flow. This provides a better at-a-glance indication of game logic than a simple list of events, and makes complex behaviors easier to accomplish and games a lot faster to prototype.
Pro Lots of resources to learn from
Epic provides multiple official video tutorials, lots of free example projects and content, an extensive wiki and regular streams showing how to use latest features.
Pro Powerful material/shader system
Allows a texture/material artist or VFX artist to create amazing effects from the ground up.

Pro Free development license, including source code
The engine, including full access to source code, is free to use; a 5% royalty is due only when you monetize your game or other interactive off-the-shelf product and your gross revenues from that product exceed $1,000,000 USD.
Pro Realistic graphics
Pro Developers have full control of the engine and source code
UE4 gives full access to the C++ source code allowing editing and upgrading anything in the system.
Pro Dynamic global illumination with voxel cone tracing decreases the computational power needed
Voxel cone tracing is a similar algorithm to ray tracing, but uses thick rays instead of pixel thin rays to be able vastly decrease the amount of computational power needed.
Pro Easy to use animation blueprints
Unreal Engine 4 is one of the best game engines. It is super easy. It dosent require any use of coding due to Animation Blueprints
Pro Spectacular lighting visuals
Pro Cross-platform editor and export
This engine exports for a big range of platforms including Linux. The editor can be run on Windows, MacOS, and Linux (Early Access).
Pro Active community
Forums have many active and friendly members that are quick to respond and help out. Even staff is very active on forums.
Pro AAA Ready
This is ready to make the next AAA game.
Pro Fast compilation for quick iteration
Recompiling an entire game to test a small change takes up a lot of time. UE4 quickly compiles in seconds instead of minutes improving iteration time by an order of magnitude.
Pro Quick release-cycle
New feature releases can be commonly expected about once a month.
Pro Professional feature set for all aspects of game development
Almost everything a game developer wants has a deep and sophisticated tool waiting for them in UE4. No external plugins are needed to make powerful materials, FX, terrain, cinematics, gameplay logic, AI, animation graphs, post process effects, lighting etc.
Pro Proven track record
Pro No coding experience needed

Pro Great tech support and friendly community
A growing community that is always helpful with dev response times averaging less then 24 hours. Often less than 12.
Pro Comprehensive WYSIWYG editor
Skyline provides a straightforward drag and drop development environment that can be customized to suit individual preferences. Playing the game and animating the scene can be done from within the editor at any time.
Future versions will allow extending editor's functionality with plugins and offer an official way of trading custom plugins.
Pro Highly affordable licensing
Skyline's commercial edition costs just £40, has no royalties or earning limitations and includes 2 activations per license purchase and a year of free updates.
Pro Runs well on lower end machines
Skyline can be run on a machine with 2GHz Dual Core CPU, 2GB of RAM and Nvidia's 9800 GT (or equivalent) GPU. While, obviously, higher specs are recommended, it's reasonable to expect around 60fps on small scenes with these specs.
Pro Excellent terrain editor
The Terrain editor is easy to use and will include features such as hole cutting.
There is a differed lighting render for internal scenes, which makes creating multi light and beautiful/atmospheric scenes so much easier.
All the tools for the terrain are in one place such as placing road/paths, vegetation, billboards, and the settings are easy to locate and change.
Planned features include:
Hole cutting in terrain and
Terrain paging.

Pro Low learning curve
Making a game in the current top engines is hard work, making something small and basic in Skyline is not. Easy to learn drag an drop model placement and editing supplemented with easy to follow video's on forum make the process straightforward.
Pro Full global illumination
Including image based lighting.
Pro Has a free version
A free version that's limited to non-commercial usage and lacks a few features is available.

Pro Impressive water render
Rendering of a water plane looks fantastic and is easily edited for different effects.
Pro Artist-friendly
The schematic editor is designed to make it easier for non-programmers to create games.

Pro Asset store
Not much in it at the moment but is starting to grow and will continue to grow with an increase of users.
Pro Constant development and regular updates
There are many additions to the engine that are on the road map such as multi threading and tree physics.
The feature list is constantly evolving with each user request and idea put forth.

Pro Support for custom editors
Skyline has a custom editor that gives the user of making their own tools for use directly in the editor to develop their games. All the editors are made using the Qt Designer and programmed in lua inside the engine itself.
Pro OSVR support announced
Open-Source Virtual Reality support is in development.
Pro More editor's
Shadow editor.
Weapon Class Editor.
Mesh Editor.
Advanced Mesh Editor.
GUI Editor.
Script Editor.
Environment Editor (volumetric clouds and day night cycle, lightening, ocean settings, height fog).
Particle Editor.
Path editor.
Schematic editor.
Navmesh editor.
Material editor.
Pro Lots of learning resources
The documentation is been rewritten and follows a structure like a course.
Introduction to > Level designer with examples > Artists
There is also video tutorials, video examples and video tutorial series been produced.
There are user created demo scenes, examples and more.
Pro Visual GUI/HUD Dditor
Making HUDs and GUIs has never been easier
Pro PBR Workflow
Full PBR workflow, your not stuck to Secular or Metallic it has both
Pro One on one private support with engine developers
Can contact the Skyline developers and they will always respond and help as fast as they can.
Cons
Con Very high build size
A blank project will build in to a minimum of 200 MB.
Con Slow
Compared to other engines, UE4 seems to perform various actions considerably slower. Actions like starting the engine, opening the editor, opening a project, rebuilding shaders, updating references, calculating lightmaps, saving projects, etc take long enough to get irritating and end up wasting precious development time.
Con Extremely long build times
Making a full rebuild, including engine can take a good 30minutes. If you plan to use Unreal professionally, you better get some licenses for Incredibuild as well.
Con Hard engine for beginners
This engine not easy for beginners
Con Steep learning curve
Especially when compared to its primary competitor, Unity.
Con No drawcall batching, performance is very bad on mobile
There's no dynamic batching support to minimize drawcalls. There's InstancedStaticmesh concept in UE4, but it's 3d only, functionally limited and requires hardware support which rules out most mobile devices.
Con C++ - oriented development cycle: slow turn-around times
The Unreal Editor is the main place to do stuff (of course), so if someone wants to do a lot of C++ stuff, the compilation and linking turn-around times can be painful. Still they probably are quite fast in comparison to the provided featureset.. Still ,they are far from optimal.
Con Poor documentation
Most of the "documentation" for code is actually just automatically generated from the source. If you're interested in knowing how things are supposed to work, you must either go to their answers site or pay for UDN.
Often their examples won't even compile, since they were written for now outdated versions.
Con Royalty based
5% of profits will go to Unreal after $3000 earned in a quarter.
Con They spend more time adding features than fixing existing ones
Con C# not natively supported
UE4 does not support C# natively, but this can be achieved through MonoUE, although it requires using the MonoUE fork instead of UE itself.
Con Poor source control support
Merge tool is not working.
Con Poor quality assurance on their releases
After each release they almost immediately release a hotfix. And another one. And another one.
Con Unreal Engine crashes a lot if you don't have the required system requirements
Con Sparse Resources for C++
C++ happens to be the main suite for Unreal, yet the documentation is very, very sparse.
Con Extremely poorly designed
The code is a mess.
Everything is connected, a single Actor is 1500 bytes, because it contains a million things that Epic once needed in a game.
Inheritance for AActor: AActor > UObject > UObjectBaseUtility > UObjectBase
Con Difficult for Mac users
If you're installing it on Mac, you simply download Epic games launcher and watch it download nothing endlessly.
Con Tutorials do not go in-depth enough
The blueprint tutorial just teaches how to turn on a light when you press f.
Con Proprietary
Con Not available on Linux
Con No Terrain Editor included
Con Bad support
The epic games team only assists with billing and account issues, not bugs.
Con Terrible physics

Con Frequent crashes
Often the editor crashes interrupting your work.
Con Poor error messages
Con Rarely works
Con Currently limited to targeting PC
Mobile targets are planned.
Con Free Version currently not available/severely limited when available.
The free version has massive amounts of features functionality removed, including the ability to compile anything standalone.
The free version is currently (as of November 2017) not available until the next major release.
Note: some of what is below is open to change, this is the coming set of changes.
The price will be jumping from $40 to £99.99 ($132.32) for the lowest tier able to build a standalone. This tier will not be able to remove the engine splash screen.
The next tier will be £199.99 ($264.66).
Con No C++ SDK
Con Small community
There is a small but helpful community that are constantly creating video tutorials and one member is creating a FREE ebook to make the transition to the engine simpler.
Con Still in beta
Not all features are fully implemented yet.
Con Lacks occlusion culling and lightmapping
This is been added in a future update, however a date of this update hasn't been given yet.
