Definately Athlon 64. Price per performance, they kick Intel's ass... even if they were the SAME price, I'd still pick the Athlon 64 since it's faster...
I've got an Athlon 64 3000+ (faster than the P4 3.2GHz in my experience) on the new low-power core, which should be overclockable to about 3800+ speeds when I get around to it... and it cost $140 Canadian
(As a matter of reference, the P4 3.2GHz costs $295 from the same store).
Plus, many of the PCI Express Athlon 64 mainboards support SLI, which is a great way to get kickass graphics performance on a budget.
