I don't know about cocos2d-iphone but I do know about cocos2d-x.
Pros:
cocos2d-x uses C++ (well, not really a pro for some but this is a pro for me)- You can easily deploy to different platforms, assuming you've set it up correctly (see below)
- It supports Lua and JavaScript, for an even easier coding
Cons:
cocos2d-x has little to no documentation. You would rely on the test projects and the API Reference. Thank god there are people like Nat Weiss who made learning easily available to users. (http://paralaxer.com/cocos2d-x-book/)- Setting up your project to work on every platform is a hassle. You'd have to be good at multiple IDEs as well as command line/terminal commands
- Most of the scripts that come with the library to create new projects are not multi-platform, meaning, you still have to set it up individually for all platforms
- Integrating third-party SDKs like Facebook, ads, and other stuff takes a lot of time since you'd have to implement them for every platform you are targetting
