I've been wanting  to have a play with either Ruby or Python while at the same time I've been wanting to do a bit of Cocoa programming.
So I thought the best way to achieve both these goals is to develop something using either a Ruby or Python to Objective-C bridge (PyObjc or RubyCocoa).
I know that ideally to get the best learning experience I would learn each techonology independently but I don't have the time. :)
So my question is which is a more mature platform, PyObc or RubyCocoa, main things I am looking for:

Documentation of API
Tutorials
Tools
Supportive Community
Completness of Cocoa API avaialble through the bridge 

Regarding point 5 I don't expect that the entire Cocoa API will be availble through either bridge but I need to have enough Cocoa APIs available to develop a functioning application.
While you say you "don't have time" to learn technologies independently the fastest route to learning Cocoa will still be to learn it in its native language: Objective-C.  Once you understand Objective-C and have gotten over the initial learning curve of the Cocoa frameworks you'll have a much easier time picking up either PyObjC or RubyCocoa.
PyObjc vs RubyCocoa for Mac development: Which is more mature?