Choosing The Right Game Engine?

If you ask me I would say it's the most important step in game development. If you chose the right game engine then your path in game development is much easier i.e. to say that a person with no experience in 3D modelling have trouble trying to use game engine dominant in high end 3D stuff like UDK 4, while someone weak in programming cannot learn Cocos and so on.....
SO WHAT?
So we need to choose our game engine properly. For me Unity is the best, and so is the case with most. Though knowledge of programming is a must but huge number of assets like PlayMaker make it much easier to use, by adding visual coding functionality. And so is the case with most features.
SO WHICH SHOULD YOU CHOOSE?
Here is a list of a few game engines each with it's own pros and cons so choose wisely. And if you are still confused jump into Unity, then you will be able to sort your confusions about the engine right here on this site with the detailed tutorials and loads of free stuff too. 
In the future>>>>>

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Unity 5

Unity 5 is the latest version of the popular Unity engine by Unity technologies. It has awesome abilities such as support for VR and almost all other platforms available like WebGL, Android, PC, Mac, iOS and even next gen consoles.

It has capabilities and features supporting both 3D and 2D development and from unity 5 on it has awesome graphics settings available. And the best part is it being so widely used it has a lot of tutorials and some awesome ones are available right here on this site(Aegit). Other than that it having such high amounts of features and customisability there seems to be no game genre out of it's reach be it Angry Birds 2, Cities Skylines, Rollercoaster Tycoon or popular Dead Trigger 2. Any one with enough programming skills and knowledge of game development can easily create the game of his/her dreams.....
It has support for C#, and UnityScript( JavaScript { not JAVA } ). Though the most commonly used language by the community is C#.

Pros:

1. Unity has a very strong community of asset and plugin creators – there’s lots of free and reasonable priced content available.
2. Support for most of the gaming platforms.
3. Deployment to multiple platforms is very easy to manage.
4. There is a free license that covers the majority of features.
5. Highly popular and an awesome asset store which provides another source of income.
6. Paid licenses are very affordable for most professional developers, available on subscription for $75 per platform currently (although some platforms are free).
7. Is best for beginners as compared to other game engines with similar feature set.
8. Unity’s visual editing tools are excellent and the editor can be extended with plugins.

Cons:

1. Has slightly higher learning curve than the simplest of game engines as knowledge of programming is a must.
2. Collaboration is difficult. Unity has an expensive asset server product to help teams collaborate.
3. Performance is not great – until very recently Unity ran almost entirely in a single thread and made almost no use of the extra cores in most mobile devices – this is improving in Unity 5.
4. The source code of the engine is not available(not even in paid version) so if you encounter any bugs you ave to find a workaround or wait for it to fixed. 

[extra 0.2 cause I use it myself]

Score:  9.2/10  overall [JUST AWESOME | FOR ALL BUT STILL HARD]

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UDK 4

UDK or Unreal Development Kit is the free version of the Unreal Engine used in many popular AAA titles. It's an amazing engine started in 2009, and been a part of development of many AAA titles in the past few years like Street Fighter V, Daylight and many more.It's had many releases the latest being the UDK 4.

UDK uses a popular programming language called C++. Which not a very beginner friendly language. It's been a favourite of both indie and major league developers for a long time now and even been used to make a movie.

Pros:

1. Huge community of helpful people and availability of lots of tutorials.
2. Multi-platform development support.
3. Free for personal and small scale commercial use and later the pay will be 25% of earnings.
4. They have state of the art tools for all aspects of game development.
5. Has full access to source code allows for huge customizability.
6. Incredible performance. The Unreal Engine was demoed using Apple’s new Metal graphics interface at WWDC. It can produce the most realistic graphics ever seen on an iOS device. The same will be true for (high end) Android devices.

Cons:

1. Bit hard for beginners to learn.
2. The learning curve for the tools and engine is significant, greater than Unity.
3. Creating anything other than a third person or first person is no child’s play and requires extensive knowledge of the engine and programming language.
4. There are no updates released by the devs of the engine but there are releases with new features thus making it hard to move the project to newer version of the engine.  

[extra 0.1 cause I use it myself]

Score:  9.1/10  overall [AMAZING | ROUGH ON NEWBIES]

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Cocos2D-X

Cocos2D-x is a open source framework for game development meant mostly for 2D game development for mobile devices and somewhat for the web but has 3D features as well. And is also used for making apps like the Antutu Benchmark app. Its been used in many popular titles like Badland, Castle Clash, Angry Birds Fight and so on.

Pros:

1. Broad range of supported platforms, particularly mobile ones.
2. Free and open source (MIT license).
3. Hardware accelerated graphics and good performance.
4. Lots of community created examples and learning resources.

Cons:

1. There’s no large commercial entity providing support and bug fixes.
2. The APIs are somewhat unorthodox. This is because of it's wavy programming language use history as at first it was Python/JavaScript then Objective-C and now it's C++ the son of the former.
3. It doesn’t do much to encourage good structure.

Score:  7.5/10  overall [GOOD AND NOT SO HARD BUT MOSTLY FOR 2D]

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GameMaker Studio 1

Made by YoYo Games it's an amazing engine made only for 2D development. It's the best choice for those who are looking to making 2D games for various platforms and have little knowledge of programming and stuff. It's the easiest engine amongst all engines mentioned in the list and still very powerful.
It has a wealth of games made in it, including Gunpoint, Hotline Miami, Spelunky and Super Crate Box.Soon I will also be adding extra description for the newer version when it gets out of beta.
And it also has a free version for those who don't wanna pay.

Pros:

1. Powerful yet easy to use.
2. Has support for Game Maker Language(GML) a scripting language(for making plugins) which much easier than C++ and other languages.
3. Has support for multiple platforms.
4. A free version is also available which is even royalty free.

Cons:

1. Game Maker Language(GML) is much slower compare to other compiled time languages like C++ and others.
2. The language is somewhat different which makes it easy but also learning it takes some additional time.

Score:  8/10  overall [AMAZING AND SUPER EASY BUT ONLY FOR 2D]

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CryEngine V

CryEngine is one of the most powerful game engines available to developers, and, with Crytek keen to welcome indies, developers can now sign up to use the engine for $10 a month, royalty-free.

The new subscription option is set to be available from May. Devs can still access the free CryEngine SDK under its current terms despite the new model.

It's primarily C++ based and really is not aimed towards beginners.

Pros:

1. Extremely powerful tool even for AAA titles.
2. Has support for C++ a commonly used language.
3. Has support for multiple platforms.
4. The payment model is truly legendary for such a game engine.
5. Likely has more features than any other game engine in the list.
6. It's visual prowess is to be acknowledged.

Cons:

1. Extremely difficult even for experienced devs.
2. It just crushes every newbie who dares to choose it.
3. Has a smaller community behind it than compared to Unity and UDK.

Score:  8/10  overall [STATE-OF-ART BUT TOO HARD FOR NEWBIES]

NOW JUST GO AHEAD AND GIVE EACH OF THEM A TRY TO CHOOSE THE ONE FOR YOURSELF!!!!