What time do you arrive? And which rental agency (so that I may suggest a route to the 105 Fwy)?

Optimal and least confusing route (non-traffic time) is:
> 105 East (you'll have to figure out how to get to a ramp).
> 110 North (staying in carpool lane).
> Exit carpool lane (before Adams exit) onto regular 110 north.
> Exit at 6th Street, and go straight off the exit.
> LEFT on Olive (you'll past Grand).
> LEFT on 5th.
> LEFT on Grand, and you're there.

There's a slightly more direct route taking the 4th street exit, but it involves different levels of streets and such.