I wouldn't worry about brand, or what kind of rails PSU uses, or use any other "rules of thumb" for that matter. I'd look at reviews of actual power supply units, find one that is well thought of, and then buy that exact model.
The same brand many times has power supplies from multiple manufacturers, so brand is no indication of quality. Looking at how the rails are designed was good when less was known about how the power supplies actually performed, but now-a-days, many review sites have come up with testing methods that show how they actually perform under stress, and that's whats important. There are multiple threads linking to these sites on the first page of this H&S forum.
If you want my recommendation, HardOCP has always done a high quality review of power supplies, and they today released a buying guide that answers your question:
http://www.hardocp.com/article/2010/04/27/gtx_480_470_power_supply_unit_buying_guide . I recommend you start there, find a model that looks promising, google it for other reviews from other sites, and if it still looks good, go buy it.
Edit: making my link into a link.
