There's 2 completely different arguments here - 32 bit vs. 64 bit and Vista vs. 7. The latter in my mind is no contest, 7 is essentially a more efficient and generally better version of Vista. There's very few legitimate reasons I can think of as to why anyone would choose Vista over 7 these days.
32 bit vs. 64 bit on the other hand - well that depends on your requirements, but it's been discussed many times before...