Duramax vs Cummins

I have owned all three, my current is a Dodge Ram 2500, so this is my opinion, not a friends or something I read on the internet.  

I don't think you will be upset with either choice of the Duramax or the Cummins period.  Engine to engine I don't think there is a real clear winner, where the Duramax does shine is in ride (mainly due to the IFS) and interior fit and finish.  My duramax was tuned and had all the bolt ons and I ended up trading it on a 1500 gaser, eeekkk I know!  Still miss that truck.  But it was essentially trouble free from new until almost 180K, I finally ripped a CV boot at about 176K.   

My latest is a 14 Cummins and I can say they have come along way since my Dad's 07 in fit and finish.  I am pleased with the truck, fit, Finish, and fuel milage so far.  It pulls like a beast, it surprisingly quiet at speed as well.  I probably won't modify this one since I am not a fan of a daily driven Cummins with after market exhaust.  Sure they sound great, but that drone if you drive it for any amount of time really wears on you. 

I wouldn't let the DEF scare you, buy a 'box' at walmart every so often and throw it in and forget about it.  It is readily available now, and the truck tells you when to add it.

Bottom line, take both for a test drive and see what feels better by your "seat O pants" meter and go with it; you won't be disappointed by either.