Use any of the majors and you'll have no problems with getting to the airport promptly. Would avoid Budget and other economy renters as they are more congested and some don't have on-airport lots.

I use Avis all the time and they always have a bus waiting to load for trip from parking to terminal. If you rent several times a year, the Avis Preferred program is available. I have never found a discounted Avis rate less than you get from the Avis web-site as a Preferred member.

Also, most majors these days check you in right in the lot with no need to visit the counter on return.