I think the Cummins is the best diesel engine available! The Dodges do not have much leg room in the back unless you get a Mega Cab (Those MegaCabs look really nice!) I have ridden in the back seat of a Dodge many times and there just is not much leg room back there.
I believe the Duramax is very close to the Cummins as far as engines go. I believe the Allison blows away the old Dodge trannys as far as reliability! So I went with a 2006 Crew Cab long bed Duramax/Allison and love it! There is a decent amount more rear seat space in the Silverado/Sierra crew than the Dodge regular Crew. I really wanted a long bed or a MegaCab would have been tempting. For a new truck I would really look hard at the Cummins with the Asin transmissions. That pairing should be every bit as solid as a Duramax / Allison!
I looked at Fords and the 7.3 powerstrokes were going for as much as I paid for my 2006 Duramax with a considerably weaker transmission. I didn't even bother to look at the new Ford 6.0/6.4's.