I second the F150 as I'm more of a Ford guy but a Chevy 1/2 ton is good too. I wouldn't bother with the smaller sized pickups, year for year the 1/2 tons can get just as good of mileage as their smaller cousins with a mid sized motor. But you will get less MPG if you decide to buy one equiped with the larger motor (ie a 350 V8).
While I recommend a 4x4 I do have to toss out an FYI. A properly equiped 4x2 with a driver who knows what they are doing will go just as far as a standard 4x4. Matter of fact, leave your 4x4 in 2 wheel drive and see how far you can get then put it in 4 wheel drive. Typically you'll make it another 50-100ft in snow before once again losing forward bite.