Well depending on what the mobo and system type you plan on building could also make a difference in which VC we would recomend and also the PSU you choose can affect which cards you could use with the setup you decide on. One thing I would advise is to make sure it has either a very good heatsink & fan or a fan on the VC cooling can be a big killer of VCs. Here is what I picked from your choices due to the fact they have 1gig of onboard memory!
http://www.newegg.com/Product/Product.aspx?Item=N82E16814129117 ATI
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127398 Nvidia
what goes around comes around
(RIG)GA-EP45-UD3P, Q9550 @ 3.5 ghz, CM's V8, HD2600XT512mb 128bit, 4gigs OCZ 1066 ddr2, Seagate sata 120 gig & a 320 gig, 2 Liteon sata DVD Burner, My DIY Case, Corsair 550watt PSU, 2ea 19" LCD monitors.