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.
ObjectiveC is nowhere near as much fun or as productive as either Python or Ruby.  That is why people want to pick a python or ruby with good Objective C access.  Advising them to learn Objective C first misses the point imo.   I have really good things to say about pyobjc.  Its ability to interoperate painlessly with Objective C frameworks is superb.  I have less experience with Ruby Cocoa and that was partly because when I last looked it didn't seem to have as clean and relatively painless interoperability.  I feel hesitant about MacRuby because it seems to go too far.  In pyobjc you can write plain python and only subclass/use Foundation and Cocoa objects when you really want/mean to.  From what I understand of MacRuby it is a Ruby on top of Cocoa.  So a string is always an NSString.  I am less happy with that.  YMMV.
PyObjc vs RubyCocoa for Mac development: Which is more mature?