--Good luck with the search for the truck! I drive a F-250 7,3 2001 and I love it! It pulls anything! We buy and sell horses, and this truck it great for pulling heavy trailers!
If you are used to work on your own truck, F150, then stay with Ford. If you've learned to work on one brand, it's always easier to stay with it since a lot of stuff is the same on different models..
What I know about the competition, Chevy has had problems with diesel pumps, and Dodge trucks aren't always that comfortable. On the other hand, Chevrolets Allison gears is great, and so is the Cummings diesel.. And yes, Fords early models of the 6.0 might be a good thing to stay away from..
Maybe have a look at www.thedieselgarage.com?
Rik