macOS RubyCocoa or PyObjc?

I can't answer your question directly, but as you will read here: (http://theocacao.com/document.page/373) both Ruby and Python will be supported by Apple for use with Cocoa with the release of Leopard.

After getting burned by Apple dropping the java bridge, I'm somewhat suspicious of how well supported these other bridges will actually be by them...

I agree with Catfish Man, although I think this sounds very exciting because Ruby and Python are truly great languages, I'm skeptical. Too many Apple technologies have been touted in some PR blurb or another only be abandoned a year or two later. If Apple keeps up its end and makes these bridges efficient and complete, it'll be up to developers to really start using them to make some serious applications, proving the technology is not a toy. Then perhaps Apple will have to make long term commitments to maintaining and upgrading them. Maybe the best thing that could happen is for some devs inside Apple to set the example by using it in some prominant Apple products. To be successful, they must keep in sync with Obj-C and not be waiting around for fixes every time Apple changes something that breaks them. As a part-time developer, there is no way I want to cast my fate with an uncertain technology, to pour countless hours and blood and sweat into something which may or may not work next week.