one or more already. I suggest a home model like Ryobi or Black & Decker.
The 10-18 volt model drill/drivers are really handy. The 24V models afford great power at the underpowered work site, but are very heavy for use around the house.
A good selection of bits would be more useful than 2 more Volts IMHO. Maybe a cheaper drill/driver with a bit set?
I want to buy a drill that has more functions, for my hubby. What is the best thing? He needs a drill and a screwdriver. Any suggestion is welcomed.