[Zeke]

You want to do the initial loosening with a breaker bar and a socket and the final tightening with a torque wrench. Therefore, you don't need a ton of power to spin the nuts quickly.

That having been said, there are many to choose from. I'd get one that will be usefull around the home. DeWalt 18v are no slouches. Ryobi seems to be selling stuff on the cheap lately and they have some good power. My favorite is Makita. I think some of these cordless drivers are getting up to the 24v range.