hands down, the MOST RELIABLE trouble free diesel would be the Dodge Cummins I-6. Followed by the Chevy duramax built by... mitsubishi I believe, then lastly the Ford Powerstroke. This is all consumer reports stuff though. Cummins has had ZERO recalls/TSBs in the last few years, followed by chevy w/ 40 TSBs, numbers are off the top of my head, then the ford w/ HIGH TSBs, and lots and lots of recalls.
I was a big powerstroke fan till I read that and started listening around to more people's experiences w/ the ford. Seems there is alot of bugs to be worked out still and lots of big problems. I was never a dodge fan but this made me look their way more in terms of diesel trucks.
The chevy will give a better ride, but the ford and dodge will have a better load capacity upfront, due to the solid front axle. The chevy has IFS. The plow shouldn't affect either one very much though because of it's relative low weight.
Cab comfort, I'm 5'7" and the back crew cab of the chevy was much more comfortable to me than the ford. I even rode in the backseat w/ a date to go wine tasting in sonoma. That was a 3 hour drive. We were comfortable. The short jaunt in the Ford to the lake w/ the boat kinda sucked. Wasn't too bad, but it sucked in comparison. Now the mid 90's ford dually crew cab was pretty damn nice. As for Dodge, haven't rode in one that I remember yet. All I know is, that Dodge Mega Cab is WAY roomy, but not sure if it's offered in the diesel. I'd look into it.
No problems that I know of in the Dodge diesel trannys, auto and 6 speed. Chevy.... I don't know much about. Not sure if they even offer a 6 speed, sure they do though. They offered two different allison autos but one of them somehow boosts the power big time, adding like a huge gob of torque using the same motor. One problem I've heard w/ the allison is, they were locking up completely, siezed up completely, like an allison ROCK, while people were driving down the freeway. So rear wheels would lock up and slid/skid w/ no warning. Doesn't seem wide spread though. Ford autos were blowing up when you modded the power in the truck too much w/o adding extra cooling and beefing of the trans. 6 speeds seem to have no problem.
Oh yeah, that Ford Ranch King in the diesel is WAY AWESOME. Super thick leather, feels really nice.