I was in a similar situation as you, but driving a 4-cylinder station wagon as opposed to a sports car. No way was it going to tow a C-Dory 22, so I had to choose something new to me. I planned to travel around for awhile, using the rig/boat as my home on wheels. Since "boaterhoming" is a possibility, I considered several trucks and SUV's. But then in thinking it over, I remembered that in times past, I have really appreciated being able to sleep/camp in the main rig (vs. the towed vehicle). Also, sometimes I figured I'd not be towing the boat, but would still want to have my "home base" with me.
So, all things considered, I ended up with a 3/4 ton camper van. I've been very happy with it. It handles the 22 with aplomb, gets around the same mileage as a similar truck, and for a camper gets "good" mileage when not towing (12 or so towing; 16 or so not towing). I really like having the van/camper space, and have used it quite a bit when not towing as well. I would consider going bigger (Class C) for long term, but for myself don't see any reason to go "smaller" (such as a pickup truck). On the other hand, to each their own so I wouldn't expect everyone to feel the same way. And too, there is a slight hassle factor in either duplicated items (dishes, etc.) or moving them back and forth ("darn, the coffee is in the boat!") when changing back and forth from road mode to water mode (vs. camping in the boat all the time).
I think one fairly universal thing is that the longer the wheelbase, the steadier the tow. Of course then too, the larger the turning radius. My van has a 136" wheelbase and is pretty relaxing to drive when towing (as that goes). I ruled out a few smaller SUV types for long-distance towing based on shorter wheelbases (would have "boaterhomed" on the road if I'd bought one of those). (They were closer to 110" wheelbase or so.)
My 22, fairly loaded up and on a galvanized tandem trailer, weighs in at around 4600# (that's including the tongue weight). I would guess that is typical.