I've owned many Ford P/Us, driven many more and Dodge as well but never owned a dodge diesel. Worked on LOTS of T444E (7.3L PSDs) and B5.9L Cummins and I'll offer the following (loyal Ford customer, but not blindly so).
Ford: The 7.3L PSD is a powerhouse but the most costly to "hop-up", the manual trans is excellant and autos are good. When you put that much Tq to an auto, expecially in pulling applications, you get some failures. Look around, a huge percentage of the RV movers use Fords and they have a strong preference for the '99 up 7.3Ls. The "twin I-beam" front suspension has been a stalwart design and is TOUGH, especially true in the 4x2s. The E4OD/4R100 and 5R110 are decent, even good ATs and will last many hundreds of thousands of miles if treated fairly. Again, anything can break unexpectedly, some do. The F-2/350s are heavy and a *little* thirstier than the Dodge, so your fuel bill will be slightly higher, but power takes fuel.
Dodge: The 5.9L is the least expensive engine to "hop-up" by far and when treated fairly they will run 300,000 easy just like the Ford. Assuming the KDP stays where it belongs, if not, you might need a block. The 5.9L excells at Tq production but is not the king of HP, the Fords pull harder under a load from my experience (same trailer with both). The Dodge Cummins will get better mileage than the Ford or GM under any conditions. The problem with them is the transmissions, both manual and autos have a terrible track record. Not saying they are junk, but they both definately have issues you may or may not get.
The glow Plugs in the 7.3L PSDs are as close to 100% reliable as one can expect to get and I've never had the heads off of a stock PSD, not even once in 15 years of working on them and only replaced one GP in that time. They are reliable and powerful, but not the most powerful you can get with a couple extra dollars and the reliability drops off fast when you start adding power. Stock, IMO they are unbeatable because sooner or later, especially with ULSD, you WILL be buying an IP and injectors for that Cummins and that's way more $$$ than a HPOP.