Those cards all will meet the minimum requirements, but only the 4850 is what you would call a modern video card out of the bunch. It really depends what you plan on doing. If you have an old computer and just have a couple of low-intensity games in mind, any of those cards should do fine. If you have a newer machine and think you'll be playing new "hardcore" games, get the 4850 or better. Would help to know the rest of your system specs.
rkwallace: Somehow, I am skeptical that a $300 water-cooled card is necessary, or a good idea for someone who probably does not have a ton of experience with that kind of thing. Personally, these days I wouldn't spend that kind of money on any card that's not DX11.