There isn't much difference between the brands, most of them are reference designs unless the manufacturer has overclocked it by default. Chaintech are good, and so is MSI, Gigabyte, eVGA, Gainward.
I'd go with Evga or BFG myself, they usually have Open GL 2.0 support and good games. Performance wise is really only dependent on the clockspeed when compairing between brands so look for the fastest speeds you can find but chances are they'll all be at about 500/1000MHz.
