I would look to a 3500 to avoid running out of payload; DRW if you plan on getting into a larger unit with high pin weight in the future.
I plan on keeping my truck a long time also so long term ownership costs (including repairs) was a major consideration for me. I chose the Cummins because it is easier to work on than the V8 diesels due to it's simpler design. One other major consideration is that the Cummins still has the CP3 high pressure fuel pump which is much more reliable and not prone to very expensive and catastrophic failure like the CP4 pump is. Ford still uses the CP4 pump and although GM has switched to another pump for 2017 it will take some time to prove it's reliability.