Yeah, it matters. Just about all the bridge chipsets are decent these days, but power supply quality wanders all over the place. Unfortunately, it's not enough to go with a known brand name because even "good" brands have poor models. Of course, the drive inside matters too, try to pick up something where they are willing to tell you exactly what is inside.
Spend some time searching through the MacRumors forums, either through the search box at the top of the page or with Google (add site:forums.macrumors.com to your query), there are many, many threads about this already.