I just got a 2012 2500 ram diesel a few months ago. I too use this as my main mode of transportation. I was hung up on the 2500/3500 deal for the longest time and must have read thousands of articles online. The tow capacity with similar gearing was only about 1000 lbs. difference and price was about 1500 bucks. All I can say is get the one that will suit your towing needs, as the mileage will be about the same. I have 3000 miles on my truck and average 14-15 mpg..and have been told that will go up after I hit approx 5000 miles. I can pull most mid sized 5rs no problem. But the larger , 38feet plus, quad slid models, you will probably want the extra payload capacity of the 3500 for the higher pin weights. I used to have a 38 foot Montana fifth wheel, weights just under16k lbs, and pulled it with a 2004 dodge 3500 SRW and you didn't even know it was there. My current camper was already in storage when I got my new truck , so I have not pulled it yet, but I did pull my 30 foot boat, a cruiser, weighs 10k and it was great.
As far as Diesel engines , drive them all, as stated, all the manufactures are making great engines now, but I do have to say in my opinion, the cummins in the dodge is the best, and has been for a long time. I have always heard that no matter who I ask. But try them all out. I love mine
2015 Dodge 2500 Big Horn 4x4 6.4 HEMI
2015 Grand Designs Reflections 323 BHS
Reese 16K Quick Slide with Factory Rail Kit Option