As for my opinion........ They are all great trucks, but here are reasons I chose the GMC,
I like the dodge, if I were to buy a dodge it would be with the manual, but I didn't want the manual. The ford is nice, but I just don't care for the 6.0 PSD. I put about 500 miles on one where I used to work and didn't like it at all.
I think the GMC has the nicest interior out of all and I do like the duramax/allison combo. So far it's been a good truck. FOr sure, the Dodge was a close second for me.