In the business I manage (Heavy Equipment), I have gone to Duramaxes (also given the fact that we own a couple of GM Dealerships). I keep a few dually's I keep around (with 175-200K) for backups, and those higher mileage units can be expensive if not maintained. And, if you plan on keeping the Truck, and you look at the long term maintenance and repair bills that Diesel Pickups do cost more to maintain-heck, one set of Injectors are scary $$$$.
Talking to the Truck Salesmen (on the GM side), there have been some reports of the 2007's having problems with the new Diesel formulation. I have one Equipment Salesman who loves the 6.0 Gas engine, but his Truck went in for a problem and he had to use a Duramax and fell in love, so I got him a new Dually (we haul a lot).
Now, for personal use, I just bought a new Z71 for myself-I don't really haul much (very little actually), so it was a no-brainer.
If you haul a lot, get a Diesel-if you don't, buy a gas rig-the gas mileage is close (comparing a 1/2 ton (19-21 mpg) to a 1 ton dually (we get 18-19 mpg)-both are Highway mielage figures, so yours may vary-I think it has a lot to do with your intended purpose-