Originally Posted by liter8
Anyone else been in this situation, trying to decide best options?
Well, having done the LAX-ONT shuttle (not by choice) you're wagering that the driver won't have to drop any LAX passengers off at home first. I did it at 2am and they still had a paying passenger

I'd personally book a cheap rental, that way you're in control. Timewise I'd guess it to be a wash, the shuttle can use the diamond lane.