They're no better and no worst then the other major agencies on a whole. Now like any agency there are good cities to rent from and bad cities to rent from (ie. Hertz TPA = Bad). I don't rent from Avis all that much, but when I have in they have always given me decent cars.
This was not at the Fort Myers Airport, however when my family and I have rented from Avis at their locations in the Orlando and Tampa Airports we have always had great service from them.
My company uses Avis almost exclusively, as does Dh's company and we use them for our personal travel. I don't know of anyone who has had a problem with them.
You might also look into the possibility of renting from the offsite location (Sears in the Edison Mall). Last year we were able to get a car at about half the price of the airport location using a code.