Dodge, don't buy it for the dodge, buy it for the cummins.
I'd actually opt for an older one.. 07 or older with the 5.9
Thoose motors are more tried and tested than any diesel pickup motor on the market, they're easy to get power out of, and you can beat the snot out of them and they sit there asking for more. I'm not a big fan of the duramax, and I wouldn't buy the first-year production of any motor, that's just me though.
Cummins. Hands down.