Generally they are fine, but we've had a couple of bad experiences with them at MCO in the past year. (We do have status with Budget and normally do FastBreak, but I've found that sometimes at MCO my paperwork isn't waiting for me in the stand as it should be.)
The first problem was utterly ridiculous: We arrived at Budget, they gave us a car assignment (which was an upgrade), and we trekked out to the space only to discover that another family was loading their things into the car -- they had been assigned the same vehicle by a different agent. So we trek back to the in-garage office, where we have to stand in line because this is a re-do; finally get up to the window and get profuse apologies and a different vehicle assignment (upgraded again), trek back out to the car, and discover it has a flat tire. So then we do the whole schtick over again (again), and finally get a car that has no visible problems, so we load it up and head out. Just as we were approaching the South Exit of the airport the check engine light came on, so back to the garage we went, to get in line yet again and get a 4th vehicle, which was finally OK.
The second instance again involved a tire. We picked up the car assigned, which looked OK, but just before we reached WDW a tire problem warning flashed up. It was very late, and we were staying near Disney Springs, so in the morning I went to the Budget office at the Doubletree to try to get a different car, but they didn't have any and could not get any more until two days later (this was a 4 day trip). The staff at the Doubletree put the donut spare on to replace the tire that was going flat, and advised me to take it back to MCO to get a same-day replacement vehicle with a full-sized tire. BUT they let me in on a secret:
The Budget employees at the Doubletree told me to go to the Budget counter on the MCO B side instead of the A side; they told me that the staff on the B side are much more responsive. It was true; the B-side counter staff jumped on the problem and even gave me a personal cell number to call if I found a problem with the assigned car in the garage, so that I wouldn't have to return to the counter. Since then, if we use Budget at MCO, I put in a flight from an airline served by side B that is flying close to my route and time, so that I can go to that side instead (we almost always fly SWA). We haven't had any more problems since doing that; B doesn't have as much rental car turnover as on Side A.