I strongly recommend getting lithium ion batteries. They're a lot smaller and lighter than either Ni-Cd (Nickel Cadmium) or Ni-MH (Nickel Metal Hydride) for the energy they hold. Lithium ion also has a very low self discharge rate and is better than Ni-Cd or Ni-MH. Ni-Cd will self discharge in about 3 months, and Ni-MH can self discharge in as little as a month.
I don't know whether it's the case with their new cordless drills, but several years ago (5-10 years) Dewalt had a high failure rate in their cordless drill gearboxes. They were using a new injection molded metal process to make their gearboxes with little or no secondary machining. Hopefully Dewalt has worked out the kinks in that process, or moved away from it.
I have a friend who's leading a group of volunteers who are restoring a WW2 bunker,
Battery 519, at
Fort Miles in Lewes, Delaware. A bunch of them are using Makita lithium ion cordless drills for both personal use and when working in the bunker. They love them and they are holding up well.
Having said that, what I'd do is go to the store and handle the drills to see which ones fit your hand well and which ones you like the balance of. My Ni-Cd Milwaukee was chosen on the basis of high torque and a handle I liked.
Try to stick with the better brands unless you're strapped for cash. (Not Craftsman, B&D, or Ryobi) Don't buy less than 14 volts. (18 volts might be the minimum for lithium ion in the better brands.)
Finally, as soon as you get your drill home put a drill bit (drill rod is better) and check the drill for runout. Some drills have bent output shafts, and some have bad chucks. It's a pain to deal with drill bits that always seem to wobble, and most of the time you see that is when you have a defective drill.