Well if you never upgrade any of the 450w+ units should do, I do prefer the fsp ax450 over the xclio 450bl, but if you are considering upgrades in the near future the zu550 is only a few bux more and gives you a lot of headroom.
The 350w and 400w units I used in office/web-surfers, the S12-330 is a great choice for a PVR or basic 24x7 system - not sure if I would use them in modern dual-core game rigs since it limits your options.