I really don't consider myself brand loyal either. I grew up thinking that Chevy was the only truck there was, would not be seen in a Ford during daylight hours, and could not care less about Dodge one way or the other. I now drive a Dodge 3500SRW with the 6sp because I thought that it was the best truck for my purposes.
Basically, each of the trucks have their advantages/disadvantages and it just depends on what you will be using it for.
The Dodge drives nice, rides nice, and has the Cummins.
The Ford is the quietest in the cab at highway speeds, rode smoother than the Dodge, has a roomier interior, better auto, and seems to have better fit/finish overall. I just do not trust the 6.0L. I'm really anxious to see the 07 and all of its reported changes.
The Chevy and GMC do everything pretty well. They have the most comfortable seats, the interior is a little aged but very well laid out, and the Dmax/Alli is a good combo.
It came down to price and performance for me. The Dodge may not win many races (which I don't believe trucks are for, anyway), but it will finish every time. If I had all of the money in the world I would be driving a F-350 King Ranch (and when the 6.0 puked I would drop a 12v 5.9 Cummins in there).