There is a small performance increase with 64bit versions. Also, 64 bit is now becoming well supported by driver manufacturers and software alike.
I have found nothing which doesnt work with 64 bit versions now and so I would big that one up. Especially as it has native support for more RAM
Saying that though... 32 bit is the safer option
It just depends if the extra frame per second or you video conversion taking a minute less makes you giddy at the knees!
crabby