I should add that renting a car to avoid having to wait for the shuttle doesn't seem like a big time saver to me. Even if there isn't much of a line at the rental place, you still have to wait for a shuttle to get there, then you have to do the paperwork there which seems to take longer than it should. Then you have to find your way to the highway. LOL.
If I didn't need the car for anything else, I'd probably to Disney express.
Renting a car out of LAX is also pricey. They add on a lot of "fees" due to it being at the airport.