I like Dollar and have used them several dozen times but I can't imagine that there'd be much difference in terms of service. Thrifty and Dollar are operated by the same company.
The trick with any of these companies is to join their frequent renter "club" in order to get preference treatment at the time of pick up. For Dollar that's Dollar Express and for Thrifty it's Blue Chip. I assume that Blue Chip works like Dollar Express but don't know that for sure. But with Dollar Express you just go over to the separate Dollar Express lane and you skip past all of those people in the regular rental lane (there are usually a lot of people in the regular lane at MCO) and the next available reservation desk staffer will take you and get you on your way to your car across the street in the garage. This cuts a lot of time and waiting.