Windows 7 is actually on par if not better than OS X right now, and it's much better than XP. However, while Windows 7 will probably run the programs without issue, if you're really worried about compatibility then you should use XP.
I think a lot of it depends on what you are going to do with windows. I run XP under Parallels on my Mac Pro so I can run autocad. It was the only program I really use.
If you are going go the boot camp route for gaming, Id go with windows 7. If you are just using Office or older programs, use XP.