I was a Chevy diesel person but switched to Ford diesels because Chevy rounded off and shrunk the cabs - for aerodynamics I'm guessing, but they felt too confining to me. If I was going to be towing a large 5th wheeler, I'd probably look at the Chevy because of the braking with the Allison transmission.
What might be the best today, might be the worst in 2 - 3 years if you're buying new. While it may not be needed, my preference for that size of a trailer would be a dually F450 or equivalent.
They're really all about the same, it's personal preference. Start visiting the dealer lots and take some test drives to see what you like. Which flavor of ice cream is the best? Chocolate, vanilla or orange sherbet?
Bill
Nodwell RN110 out moose hunting. 4-53 Detroit, Clark 5 spd, 40" wide tracks, 10:00x20 tires, 16,000# capacity, 22,000# weight. You know the mud is getting deep when it's coming in the doors.