ATI vs. Nvidia

Which would be better for a vid card? And whats a good card to use in the following system for under $200.
Pentium D 805 Dual Core
ECS C19-ASI Nvidia nForce 4 SLI XE ATX ( May have to change if using ATI)
1 Gig of Corsair PC3500 DDR2 SDRAM (Board will support up to 16GB?)
Hitachi Deskstar 160GB 7200 RPM SATA HD
Thanks,
Aaron
Pentium D 805 Dual Core
ECS C19-ASI Nvidia nForce 4 SLI XE ATX ( May have to change if using ATI)
1 Gig of Corsair PC3500 DDR2 SDRAM (Board will support up to 16GB?)
Hitachi Deskstar 160GB 7200 RPM SATA HD
Thanks,
Aaron