Mike, both trucks will serve your needs just fine. I'm coming from a '91 F-350 and it got the job done... a little slower in the hills.
I was looking to replace my '91 this year, and looked at all makes. Didn't want to risk the 6.0h no from Ford, and I'm just not really into GM trucks... too squishy. I test drove the Ram and fell in love. Stiffer ride, just like my Ford, and the Cummins was a huge draw.
For me, the Allison of the GM wasn't a selling point--I've replaced 2 automatic transmissions in 2 vehicles in 2 years. The new Ram 3500 I've ordered will have a six speed manual transmission.
SO it came down to ride feel, engine, and overall impression. Dodge won the first and last. The engine is up to debate, perhaps, but I'm no fan of Isuzu (from which the Dmax design comes.)
Someone else can chime in on mileage and the availability of comparison tests.
Price and the quad cab sold me on the Ram. With the front seat back to my liking, I can sit comfortably in the back seat. Couldn't do that in the Ford or the Chevy, and a crewcab wasn't an option--been driving one for several years and they're bigger than we need. The Dodge folks were willing to deal--got the Ram for $34k, almost loaded, and that included a $2000 nav/stereo system.
Mike