Without invoking brand wars, here is my take after having owned two chevys and a ford, as well as working for a company that had a fleet of dodges and a fleet of Fords.
The chevys I had were hand-me-downs from my dad who is a die-hard chevy guy. One was a 98 6.5TD, the other an 05 Dmax/Allison. I love the Dmax. The allison hasn't proven to be too reliable in its as-delivered tune. In typical fashion, GM took a bulletproof tranny and softened it up so the old folks wouldn't complain about rough shifts and somewhat neutered its reliability. The aftermarket has solutions that make it absolutely rock solid, so I would suggest those mods if you tow alot. if you're just towing 5000 lbs, don't sweat it, but if you're going to be doing a lot over 10k or power mods, I'd consider upgrading.
The fleet of dodges we had were 24v cummins, mostly 01-02 models. They were bulletproof. Some of them had nearly 400k on them, with long idling spells and PTO use. We sorta sold them more because bean counters decided that there was a tax advantage or the rate of depreciation and potential for repairs was risky. So, a whole new fleet of 6.0 powerchokes was ordered. I have one word for you; don't. No real word on the new 6.4s, but I'd be wary.
The new bigger cummins is pretty much hated in the circles I travel. Unproven reliability (not so much in the engine itself, but all the crazy emissions stuff) has stifled the love. Who knows, it might be nothing, but the guys I know are currently scouring the country looking for the last of the smaller cummins before they're gone. As of this summer, they're scarce.
I personally want the reliability of the upgraded allison, the styling and ride of the chevy, the interior comfort and overall quality of the ford, and the cummins from the dodge. Is that too much to ask?
If you're buying a daily driver that tows a little, I'd suggest the Dmax/Allison, but the little foibles of the chevy truck bug the heck out of me. For instance, my Dmax truck, no matter what you do, when you turn the key on it starts playing disc 1 on the radio. It could be off, set to FM, or playing disc 3, but it always goes to disc 1 when you turn it on. The interior lights sometimes won't shut off, the trailer wiring is awful and completely unreliable despite trying multiple connectors. Frustrating to say the least. The A/C on every GM I have is totally inadequate if you're stopped. Die-hard chevy owners like my dad who wouldn't dirty his butt in a Ford has never had the experience of a truck without all those little issues so he thinks its normal. If you're buying a purpose-built tow vehicle and don't mind the lower-rated ride, comfort, and ergonomics, I'd go Dodge. If you're most concerned about creature comforts and truck reliability and aren't too concerned about the reliability of the engine, go Ford.
That's my opinion and I'm sticking to it.