Ok, it's true the Cocos-2d is the more powerful, but I have used Sparrow http://gamua.com/sparrow/. It has a smooth learning curve, and you can develop a game within days!. It integrates with other important frameworks, like Box2d (http://www.codeandweb.com/blog/2012/05/07/physicseditor-sparrow-box2d).
Regards.