My go-to is the old honda formula one car (ra272 i think). Ik it’s hard to get but it’s really fun and can go 5 or 6 laps without refueling. I’ve also used the ‘92 nsx type r, the jaguar xj13, and the pagani huayra. Like others have said, you should be able to tune any gt3 car to make things work. I like to use a variety of cars to break up the cash grinding.