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It's going to depend on what your using it for, and how you're using it, and what you like...

The Duramax is Powerfull & Quite, and now has been out on the market long enough to see that servicing them is not a nightmare once they're off warrantee.
The Cummins is legendary for reliability and good power (especially once chipped, etc.) however the Dodges are also notorious for having the cab's litterally "rattle appart"
The Powerstroke is a good work-horse, made in a joint effort with Navistar (International) and the Blue Oval Group. Some have had issues with an oil o-ring seal on the oil-rail, more issues with cold weather and repeated cold starts. Good unit. Not as loud as the Cummins, but not nearly as quite as the Duramax. Also the Ford has a much more "Truck Like" suspension and ride. Doesn't seem to be as refined as the Chevy/GMC.
That being said - the oil patch is full of all three makes, any one of them can be found in company fleet's that go off road. All of them get the crap beat out of them and seem to survive for a limited life cycle.

Personally, I'd suggest taking each one for a test drive and see which one YOU like best.

I would venture to guess that if you're asking for a dulie then you will be towing?
The new Fords do have a built in electric brake controller that is VERY slick - modulates the trailer brakes extremely well. (Don't know if either of the other have that.)
During your test drive, I'd also suggest that you tow your expected trailer with payload. Some dealers will not let you do this, but if that's what you're going to be doing with it - then you'll need to know how the truck acts under load & pressure.

Also, the max GCVW on each of these 1 ton trucks is does not differ very much from one another, nor do they really differ much from the single wheel versions. From the last one I was looking at, there was only a difference of 500lbs GCVW. The biggest advantage of the dulies, if you don't need the extra little bit of weight, is the stability of it. (You're extending your lateral wheel base or stance of the truck and will be more stable with a higher or heavier load.)

The next thing to consider is the actual weight you're going to be towing/hauling. If there are different options for final-drive gear ratio's, you'll want to choose the right ratio for the engine speed & power output based on your specified crusing speed and transmission & tire size. (I also like that the Chevy uses an Allison Tranny!)

ALSO: If you're only going to be using this as a tow vehicle, and really not much emphasis on the daily driver portion then you may be able to consider a truck that would be considered more of a commercial application truck - quite often less expensive than the "luxury work truck". Examples of this could be: International MXT or CXT or 4200, Ford F450 or F550, Sterling 3 ton (looks and smells like the Dodge Pickup).
I'm sure there are probably a number of "Toy Haulers" out there that you may be able to pick up for a reasonable $$ and still keep your daily driver fun and maneuverable...