I will always go with the 4WD, over the 2WD. For some the extra height might make a difference, but that is the only disadvantage I can see. The front end on a Dodge/Cummins truck is so heavy it tends to sink in damp grass or anything other then blacktop, the addition of front wheel drive gives it an advantage over the 2WD. Obviously it works better in winter conditions, but also in the summers sand, where weight and low speeds make for slippery starts. I also like the fact that I can put my transfer case in LOW range (2Wlow kit to disengage the front axle) and have extra power for steep or rough conditions, or back the trailer slow with little effort and stress on the truck.
Some will not like the taller truck because it might ride a little high for some trailer types. This is a valid point, but like anything else it can be over come, just depends on how much effort you are willing to put forth. Also some will contend that the 4WD trucks cost more to maintain, this isn't an issue in my book, they are about equal.
Mileage, this I don't know. We have members that get as high as 28 and as low as 8, just depends on who you ask, and how much BS they contain?
It will always come down to the individual, I am sure most that ask a question have 90% already made their choice, they are just looking for some back-up. People seem to be polar, they are either auto or stick, pick-up or car, diesel or gas, 4WD or 2WD. So I guess the question is, What are you? Since you will be the one paying for the truck, you should get the one that fits your style.