Here in my area the Fords are the most popular, followed by Dodge and Chevy. Individuals in the construction trades and in farming seem to be the biggest users, most of them being Fords. I'd be willing to bet that the Fords outnumber the Dodges by just about 2 to 1, and I don't see many of the Duramax's, though their numbers seem to be climbing a bit. I am also seeing more CTD's than I was a few years ago in comparison to the Fords. As for heavy towing, I would say that I see nearly equal numbers of Fords and Dodges, very few Chevys.
Most of the Ford guys I've talked to bought the Ford after a number of considerations, one of them being price, and we have a LOT of Ford dealers around here compared to Dodge dealers, so service availability was a big issue for them as well. Most of the Chevy guys that I know don't tow heavy, usually pulling a boat or snowmobiles at most, and they wanted to get the mileage of a diesel but did not like the noise associated with them up until the last few years.
I hate to make this long, but I gotta tell you about one guy that I believe I have converted from the Ford camp. I farm on the side, he farms full time. My son dates his daughter, so I end up giving them a hand once in a while. Last summer we were pulling haylage wagons out of a field that has a steep hill going from the field up to the road. These wagons weigh 10 to 12 tons when loaded, and farm wagons don't add any weight to the tow vehicle to help increase traction. Well, we were out in this field and there were two identical wagons sitting there to be hauled back, so we went to get them. We both hooked up and he took off first, got part way up the hill and he spun out. I had to unhook, get in front and hook up a chain and drag him up the hill. He expected that he would have to do the same for me, but that was not the case. I pulled mine up without slipping a wheel. Needless to say, he was impressed.
Now, I don't know for sure what he was up to, (he hasn't said anything) but last week I saw his Ford sitting in the customer parking at the local Dodge dealer. No new Dodge yet, but since he does not currently own any Chrysler products, he couldn't have been there for parts, and he did say that he was considering getting a new pickup this year. At least I've got him looking anyway!