I would agree with this assessment.

LAS has all their car companies in their new Gulag/centralized location.

ONT is on the way from LV to almost anywhere in SoCal.

LAX has a LOT of variety, but you may have to walk a few blocks from one rental agency to another, as they all maintain different lots (with Hertz being the furthest)... only way to connect shuttle-to-shuttle is to take it back to the terminal. Also, if you swing from LV through downtown LA and onto Hwy 1, LAX is a bit out of the way.

BUR may be another option, but the fleets are way smaller.

SNA may be useful if you come this far south... plenty of variety, and all the majors are on the basement level of the parking garage across from the terminal (easy freeway access too).