I much prefer windows 7 64 bit over XP. However, if some of your hardware does not have drivers for Windows 7, then that will be a issue. Fortunately, most of the mainstream hardware does support it, but older scanners, and older cameras that use firewire do not have 64 bit drivers.
I did not have any issues with my hardware.
If you want to use a SSD, for example, get Windows 7.
Agreed windows Xp does not support trim. Win 7 flies on ssd. You can get a 128gb Samsung 830 for $90 for your os and out a nice wd 2tb 7200rpm sata iii drive for workflow. Done.