Since I have owned a Ram, F250 and spent many hours in a Duramax, I have to say you need to drive them all and see what you like..
The Ram handles the best, I love the steering on them. My 3500 dually 6spd got 23mpg city and about 26 highway and with a programmer it would spin the tires from a 45 roll. I love the fold down center console and the seats are very comfortable. Personally it's the best "driving" truck out of the three, it's also the most powerful tuned. The back seats are very small and the trucks start out kinda pricey. The interiors SUCK on the 06+ trucks but the 2010 leather interiors are amazing. The black cloth 03-05's though are very nice and comfy, mine was an 05. Uses quite a bit of fuel idling all night.
The f250's have the most room inside, I personally LOVED the 6.0 but the EGR will have problems. Straight piped it has that awesome muscle car roar. It got about 12 city and 19 highway, very tight driving truck but had a cheap lift so the ride was terrible. Idling all night would use like a gallon, I use to sleep in it all the time. It's surprising it uses a hell of a lot less fuel then the dodge idling, fords also seem to have the best A/C. I did start to have some egr issues but I cleaned it out and ran fine. I beat the living **** out of that truck every second I had it and it barely gave me any problems, very well built truck. They are notorious for ball joints though, which mine was needing.
The duramax is like a good overpriced mixture of the F250 and dodge. Just as powerful as the ram, fair gas mileage at about 16 city, 22 highway driving it hard and it has a fair amount of room inside. They handle good, drive good and just seem to be a good overall truck. My friend had a lot of issues with his but he was not easy on it at all.
I'd say the best bang for your buck is an F250, I loved mine and would give the world to have it back. And don't be scared of a 6.0, it was so much more powerful then my 7.3, and the ford transmissions are a lot stronger then the allison. Go ahead, flame away.
Whenever you get bored of your truck, get a programmer, it's so damn fun whooping Camaro's and vettes with all your buddies in a 3500 hot shot dually haha. In my f250 we'd put it in 4hi and launch on ricers and even a few vettes. My friends Dmax stopped a 350z from a stop with the truck full of kids lol..