I think you have to decide if you want gas or diesel. Best gas 3/4 tons will be a Chev or gmc 2500 with the 6.0 4l80e combo. One of the most bulletproof combos out there and replacement parts are cheap and the truck is easy to work on. The F250 with the 6.2 gas motor is also very good but a bit harder to work on if you do your own work.
As far as diesels, the 5.9 Cummins I think is the best. If you can find a manual 6 speed that is what you will want. The 7.3 powerstrokes are great too but they are not near as easy to work on as the 5.9. I have owned and worked both. The 5.9 is an inline 6 motor and those are very easy to work on and maintain. Lots of room in the engine bay. The 7.3 takes up every inch of engine bay and you gotta take a lot of stuff off to work on just about anything. The 7.3 will last forever but just doesn't have the power the Dodge has if you leave them both stock. If you go 7.3 a small tune will do wonders and wake up the engine.
The person that stated the 6.0 is junk was probably referring to the 6.0 powerstroke, which from the factory was a turd. Can be made into a good engine but was not very good from the factory. The gas Chevrolet 6.0 is one of the best had motors ever made, I currently drive one.
