Yeah I like nvidia better too, the first ATI card came with my P4 system, some all in wonder card, can't remember which one, but it didn't really run SC4 or GTA3 pretty well. Replaced it with a evga geforce 5700, and runs the games alot better.
Though as far as going AMD, thats up to you, I don't have any experience with AMD, or know anything about them. Not sure you can tell but I've only owned Intels other than my 1st computer which was a Commodore PC. From Pentium 66mhz, PII 450mhz, P4 northwood 2.2ghz, and now Conroe 2.4ghz.
C2D E6600 @ 3.15ghz w/ 1.35 vcore
2GB G.Skill DDR2-800 (4-4-4-12)
XFX 7600GT xXx