If you had a short wheelbase vehicle, I'd say get the short trailer for sure. But with that pickup, it's not much of an issue.
I started with a popup, for just one summer. Didn't like it. Then a 23' Rockwood, nice but had to sell (2007) due to wife's med bills. She won't camp any more, so since then I've had a 17' Burro, then a 16' KZ, then a little Aliner. Now I'm camping out of my Li'l Hauley cargo trailer (an empty Snoozy shell). The Burro and Hauley tow noticeably easier (a couple mpg's higher) than the boxy trailers; they are more rounded, more narrow, and shorter so the wind resistance is less. Wind resistance will matter more than weight to a great degree for highway-speed towing.
I would recommend a TT that allows a full time bed (so you don't have to make it daily) and a comfortable place to sit (those upright dinette seats are the pits after a couple hours). A front bunk, side bath Scamp 16 would work; you can leave the dinette made up as the bed all the time, have the front set up as a 'sofa' and use a tv tray type of table for eating up front. The back cushion is canted so it's more comfortable. If you buy a boxy TT, I'd say try to keep the width at 7' or max 7.5'. Oh, and no slideout. JMO.
BTW, that KZ I owned for 3.5 years and it developed a roof leak shortly after I sold it. I felt bad for the new owner and went halfway with him on a re-seal.
