I just want to know, that in the long run, using which of these engines will be better. Although I feel that using Cocos2D will be a better option, as it can also be used for iphone development, there's just 1 tutorial http://dan.clarke.name/2011/04/how-to-make-a-simple-android-game-with-cocos2d/ which I've found so far. libgdx, on the other hand has a complete book.
Consider using AndEngine. From a short look at libgdx, they seem similiar (Although AndEngine is 2D only). However, AndEngine has everything you need for a 2D game. The only thing it lacks is documentation, but it is open source - if you don't get something, take a look at the code.
There is an active forum here, and there is also a SO tag for AndEngine, so you can ask questions here too.
It also has many extensions for useful add-ons, like the physics engine Box2D which is a 2D cross platform physics engine used for many well known games (For example, Angry Birds uses it). It also supports TMX tiled maps, with a pretty easy interface (Actually that's the game I'm developing now, it's really easy to use the AndEngine TMX utillities).
So.. before you pick one of cocos2d or libgdx, take a look at AndEngine :)
@Greg That's not true...
It is easy to learn and good documented engine
There is almost no javadoc at all. But the forums are full with tutorials, and so is the web.
EDIT: From your comment at Greg's answer, if you are looking for easy developing, AndEngine is a good choice. From taking a look at that's cocos2d tutorial code, it seems much more complicated and less intuitive than AndEngine's code.
I will suggest libgdx too. It looks more promising than AndEngine.
I've tried both Andengine and libgdx. Have not tried cocos2d. Andengine performed really poorly. The main advantage I get with using libgdx is that you can run your app on the desktop rather than on an emulator or device, which makes iteration times much faster, which is essential for game development. If cocos2d can do this, then I think it's fair to use, but rapid iteration is definitely what sets libgdx apart from Andengine.
i'm currently developing a game and i started with cocos2d. I struggled with it's coordinate system. Then i tried AndEngine, it was nice, but i was afraid of performance. So i switched to libGDX and im happy with it. It might look a little low level, but i think that you'll switch from other engines to libGDX eventually.
I am a newbie to both android game develop and libGdx.
By my 3 month experience, libGdx is quite fun.
Lots of demo, not bad document, and forum.
And Coco2d seems stop developing and the main developer has changed to use libGdx.
So I guess libGdx maybe a better choice.
I am currently using libgdx for the box2d physics and also cocos2d for drawing and scenes. It is very useful and I highly recommend it.
andengine is only use for student,it easy to learning,hava alot of example but the performance very terribel,and it can not fix. :( if u continue using andengine for developing commercial game,u will be disapointed
来源：https://stackoverflow.com/questions/8552176/cocos2d-or-libgdx-for-android-game-development