Getting a rental car from the Cleveland airport is really easy. Just hop on the rental car shuttle, and you're taken to an offsite location where all the major rental car companies are housed under one roof. I went with Budget b/c they have incentives through upromise.com
The only issue I had with Budget was the rental car. I rented a Pontiac G6, and when I was driving it, the engine didn't sound good. Granted, it was a Pontiac, so who knows? Whoever had used it in the past put a bunch of dents in the car and busted out one of the airvents on the dashboard.