I think the fit when I sit is the first most inportant thing.
Next would be the bowl I like porcelian over plastic, and I dont know if your choice is a plastic bowl or glass, glass is easier to keep clean.
the biggest thing I have found with Thetford is they skimp on the waist gate and water flow peddel some use the flipper and mine uses the ball type gate, which I like better, no more coat hangers to remove TP in the seal.
All in all I like the toilets that are being installed now in the Monty's it looks like a marine type toilet. which will be my next choise.