The ONLY reason why I got the 32-bit version of Vista was because at the time, drivers were rare. I got it way back in January when it barely came out. Actually, I got mine before anyone got theirs because of my work.
Otherwise, I would get 64-bit Vista. 32-bit is the standard now (so you really have no choice here unless you go up to 64-bit).
If you want Vista, it's 32-bit. For the enthusiast, 64-bit is the way to go.