I spent some time looking at all three about a year ago.
With a gooseneck and a dually in mind, even though I was raised as a Dodge guy I was looking very hard at the Ford and GM products. We wanted a crew cab, and the backseat on the Dodge was just a bit too small. (My parents have a 1/2 ton version of the current quad cab.)
With the advent of the Dodge Mega Cab that is MUCH better, but I believe they sacrificed bed length to give more legroom. Not sure what the bed options on a dually are with the Mega Cab. (A friend looked at one and, although he says he hates Dodges, nearly bought one, so that says something for the improvement they made.)
I wanted a full 8' bed for a gooseneck - not knowing exactly what I wanted to pull with it, it eliminated any issues with the corner of the trailer and the rear window that can crop up in a shortbed.
Engine wise, joeg is correct - the Duramax and the Powerstroke have had their issues....but the early 6.0 in my Excursion is cruising along just fine 2 years and 32xxx miles later, so a lot of it is luck. (Hope mine continues.)
I LOVE the TorqShift tranny in my Ford....the Allison in the Chevy is, as I understand it, similar in function. Haven't heard a lot about the new trannies in the Dodges....which, based on their late-90's issues, is probably a good thing.
Jarrod