I've used Cocos2D, and it was great - I've been meaning to write some posts about it, haven't got around to it yet. I haven't used other frameworks, so I can't compare, but for a simple 2D sprite game Cocos2D was a great way to hit the ground running.

Video of me making the game:

http://www.youtube.com/watch?v=se2mi_kfUko

I'm far from an expert, but if you have any questions I'll try to answer them.