Apples to apples condition, as long as your talking LMM Dmax and '14 up Cummins 2500 or '13 up 3500, it's a tough call.
My take is yes there are some reported disaster repairs with the new injection pumps on the Dmax, but I'd take an Allison trans over the 68rfe in the ram. Never drove an Aisin truck though.
I wouldn't have reservations about either of them personally. I do like the '15 updates to the GM twins though and now they throw the LP5 in there for '17 which is a monster, on paper. Haven't drove one, but I had an old LB7 tunes to similar power levels and it was a sweet combination and FAST!