On the Mac, I mainly use Safari, as it happens very rarely to me that a website doesn't work with it. Even my banking site works fine, allthough I have to admit that it didn't until the last Java update from Apple. IE on Mac definitely is crap, because it is old and didn't get any development since years.
On the PC, I use Mozilla or Firefox, because of IE's security flaws, no tabbed browsing and I just simply don't like the fact that Microsoft integrated it in the OS so much that you can't use Windows without IE. On the Mac, I can throw away Safari whenever I want, and it will not affect my system. I just don't like the way MS forces people to do things, without being an Apple fanboy.