We have neoprene. Really easy to take on and off, no straps to tie, and they don't move around sliding in and out of the car. They are really and hug the seat, so if the lumber support of the seat is good, this isn't lost like a 'bulky' lambswool.
Downside is if you've had a wool cover or the like, sweat is absorbed and you don't feel it. The neoprene doesn't, so sweat sits between your back/legs so it feels like you are more sweaty than in lambs wool etc.
if I could afford a tailored lambswool I'd go for that, the tailored neoprene are about a third of the price so that's what I've got.
Haven't used canvas seat covers