I travel approximately 10-12 times per year, and usually book my rental cars through Priceline, which generally places customers with one of the larger rental companies (Hertz, Avis, Budget, Alamo, and National). In every case, I've never had a problem, ending up with clean, well-maintained, low-mileage vehicles (in September, I ended up with a loaded, 2010 Pontiac G6 with 250 miles at the Alamo location in Baltimore) at very attractive prices. Yesterday, I found myself stranded at the Fort Lauderdale airport without a reservation, and Thrifty was the only agency that offered a decent rate to walk-ins ($46 per day for a compact). I was given a dirty 2008 Dodge Caliber with 41,000 miles on the odometer, but as I was in a hurry to make a meeting, I decided to bear with it. My first surprise came when I tried to open the window and hand my rental contract to the security guard--I couldn't find the power window button. Turns out that the vehicle had manual, crank windows and no power options whatsoever, which I've never seen in the last ten years of renting vehicles. When I finally got the car on the road, it begin to shimmy at 45 mph, and by 60 mph I could barely hold the wheel steady. Thrifty's road service representative advised me to return the vehicle immediately for a replacement, which turned out to be a 2008 Ford Focus with 43,000 (!) miles. Although the ride was much better, the tires were clearly unbalanced, and the interior had a strange odor. Sadly, another unpleasant surprise was yet to come--when I took my bags out of the trunk, I noticed that the entire trunk liner was soaking wet and smelled of mildew.
Bottom line: avoid Thrifty at all costs. If you can't get a car from one of the larger companies at a good price through Priceline, Hotwire, or some other discount service, you'd be better off eating the extra cost and renting from them anyway.