Well, personally, if your going the Dakota route, I would try to find Quadcab with a 5.9 engine. Mileage will suck, but you'll have more power on tap. As for towing, well, there is an elderly couple in my area who tow a 28" 5th wheel travel trailer with a quadcab Dakota. It's a 2000 model, I seen cruising down the interstate many times. My 2000 Quadcab (124K miles) is rated to 6,200 lbs towing properly equipped. One area where you will have a problem is that lack of aftermarket love and support for the Dakota. The front end sadly won't handle to weight of a plow. The reason so many people will knock a Dakota is lack of aftermarket support. BUt, by comparison, a quadcab Dakota vs. Frontier vs. Colorado vs. Tacoma, until about '07 the Dakota was the largest interior wise, since then, they are tied with the Tacoma but still larger than the other two. Co-worker just bought a '08 Frontier 4-dr, doesn't have the space of the Dakota and entry/exit is tighter.
Towing with the 1500, again, properly equipped they can handle 6,000 lbs to 7,000 lbs easily. BUt a comparison, best friend has a 2000 1500, 318 v8 and 5 spd and tow package. The weak link is the 318 and the manual, he is only rated to 5,600 lbs. He recently upgraded to a NV4500 trans and some other engine mods, he tows a 5,000 lbs travel trailer and feels more confident now with these upgrades.
If you got the diesel route, find one that is pre-DPF emissions, hence a 5.9.