I use a corded one, but have used the cordless one somebody gave my Dad as a gift. Doing anything that requires some time, the cordless one's power seems to fall off. I'll stick with the corded one.

I use a cordless driver though - a 3v Lithium and its amazing. I've had it over a year, use it all the time and only charged it twice. There is no speed or torque difference with it fresh off charge stand or using it for couple of months.