Always book ICAR (Midsize) for EA/ES access (on the National website it should say "Executive Eligible" when selecting the car class, assuming it's an Aisle location).

Regardless of what you take from the ES, you'll still pay the same ICAR (Midsize) rate... doesn't matter if you take a Malibu (FCAR), Impala LTZ (PXAR), or a Tahoe LTZ (FFAR), you'll still pay the ICAR rate.

Also remember that as Executive you can book a PCAR at the FCAR rate (it won't show the discount on the class selection page but will on the summary page before final confirmation. With a PCAR reservation you often have a chance at LCAR or better if there aren't any PCARs available, and you can also take something from ES and have them change your rate back to the lower ICAR rate at the booth when you exit (just tell them you took something from the aisle and need your rate adjusted down).