I'd say the Athlon 64's take the cake in gaming
they are the best performing CPU's in benchmarks and will handle anything you throw at them
My friend is in the process of building his PC, and the only thing he hasn't got so far is his Athlon 64 3800+
he got a GeCube Radeon X800 Pro VIVO and he soft-modded it to an XT by flashing it and putting in the XT's BIOS
he tried it in his Athlon XP which usually gets less than 1000 in Futuremark, and he got about 8300, then when he flashed it and put in the XT's BIOS he got over 10,000 - it's a bloody awesome card
- anyhoo, go Athlon 64, and if you can, go socket 939 as it supports dual channel memory