I'm building a new PC and want to move on to a 64-bit OS, I hear good and bad for both XP64 and Vista64 such as...

XP-64 has poor driver support but better backwards compatibility.

Vista will support DirectX 10 when it's out, but is a resource pig.

If you're using either I'd like to know which you think is better and why.

Well Vista is a resource hog but if you're looking to go to 64 bit I'd assume that's because you want to use 4gb or similar. Thats the only real reason anyone should at the moment. Vista's resource needs should be addressed by such a system and provide directx 10 support like you've said. So I'd say Vista.