"Hi" Janell and Welcome to the DIS boards!
Yes, Avis is onsite at the Orlando Airport (MCO). We have rented from them many times at Orlando Airport and never a problem. My husband likes to rent a Cadillac while on vacation and Avis has caddy's as their luxury car. We are renting from Avis again next month. Also onsite at MCO are Dollar, Alamo, National, Budget and L&M. The only one I don't recommend is L&M, stick with a nation wide rental agency and you should be fine. If you need a discount code or coupon for an Avis rental, send me a PM (private message) and I may be able to help. You can check mousesavers.com for discounts on rental cars at MCO too. Good Luck!