I had a 8000 lb TT that towed like a dream. Easy, straight, with a mild ride. Sold it and bought a 14k 5th wheel since its what we always thought was the best way to go and we needed more room. 5th wheel is much heavier so the truck now rides much stiffer, and the chucking can be an issue if not loaded perfect. Thats not to say that everything about a TT is great, but that I now know the pro's and con's to both setups.
But if you're after a trailer that can handle rough off road conditions, I'd say that a TT is less likely to come in contact with the truck.
Ride wise..... A 4wd is always going to ride somewhat rougher than a 2wd. Just for sake of more unsprung weight in the front suspension and stiffer suspension.