If you want a reliable diesel truck, this guy says these are extremely easy to work on and reliable.
It's mentioned as the last of four diesel trucks to buy in this video.
The 250 is a 3/4 ton and the 350 is a 1 ton. There's a huge difference with the 1 ton being a dually (4 rear wheels) and towing capacity.
In my opinion, the ideal setup to tow a large trailer is the F-350 with a flatbed and gooseneck hitch, plus another regular hitch with a 2" ball (or even a 2-5/16"), maybe with a pintle hitch. You'd be able to tow any type of trailer other than a big rig