Ask 10 members of Air Forums about tow vehicles and you will get at least 10 different answers!
Choice between a 250/2500 and 350/3500 will be dependent on what else you want to haul in the truck. For anything but the largest loads, the 250/2500 will be fine. But do the math. Add up the people, cargo, tongue weight and hitch and compare with the payload capacity.
I pull my 30' Safari with a 2012 F150 4x4 Supercrew Ecoboost with all the towing and payload options. The Safari looks to be about 1000 lbs lighter than the classic - but given the ease with which I can tow the Safari, I don't think the extra 1000lbs will make that much difference.
No major mountains yet - that comes next summer.