Your title of the post and your question does not have any relation..
What is the best programming language to use to make application for Mac OS X?
How can you say that a particular programming language is best for a particular OS.
The programming language that you need to use depends on the type of the application you want to develop.Some languages are best suited for some features.
Overall , every programming language has its own uniqueness.
as harinath_2007 said, it depends on your needs. but, mainly C++ and Java can be considered as most powerful and popular cross-platform programming languages. again, it depends.