I only like to talk from experience, so I will tell you that I currently am using the Milwaukee V28 1/2" cordless hammerdrill.
I like the drill a lot, I highly recommend looking at cordless drills that use Lithium-Ion batteries. The Milwaukee has some unique features such as the battery charge indicator built into the battery itself. I find this a real bonus being able to double check the charge on the battery before starting a large job, in case I need to start charging a backup battery. Milwaukee also makes one of the better belt clips I have seen.
I used to own a Metabo 15.6V drill. Very nice drill too although Lithium was not out at the time I had this drill. Interesting IMPULSE feature, helpful in starting holes on metal while preventing the "skating drill bit" (yes sharp bits help too - thats why I bought a DRILL DOCTOR, thats another topic)
Also have used the Dewalt 18V (older than the new XRP) and found it to be quite capable. Lasted about 3 years.
If I was to buy a drill tommorrow I would give serious thought to Milwaukee's new V18 line of tools... all the nice features of the V28, just a lot lighter!
Still waiting for a V14or V12 Milwaukee!!!
I don't think I'd ever consider Dewalts 32V lineup unless I was building decks for a living. Tried one at a local depot store... they are on the heavy side of what I would consider a good drill for daily use.
I have also given serious consideration to HITACHI in the past - they make some nice new Lithium powered tools, they also have a unique charger that can convert your cordless tool back into a corded tool so you can finish your job without waiting for a battery to charge.
Panasonic has a nice drill - when I looked at it it had one of the largest AMP/HR rating on the battery (not sure if this still holds true) Their battery was one of the top batteries at the time.
Hilti make excellent drills / tools although some may find them a little high priced.
Knowing their OTHER tools, I am sure BOSCH makes a good competitive drill as well, although I have never personally used one yet.
For me, the must-have options in a cordless drill:
Lithium-Ion (or newer technology in batteries)
Weight - 28V Lithium or lighter (18V cordless or less preferred) lbs ?
Chuck - 1/2" ratcheting
2 Batteries or more with 1hr or less charging option.
Service - Good Warranty / Local repair depots / serviceable parts (brushes)