I have used Thrifty all over the world (slight exaggeration)

I have had niggly problems with them, as I have with Alamo, Dollar and Budget - I would put all these suppliers on a par - not perfect but generally okay Watch out for, the hard sell on the upgrades and make sure you know what coverage you have in case they try to sell you extras you don't need.
Thrifty is now found with all the other firms in the RCC (Rental Car Centre) at MIA so again there is nothing to differentiate them there - if they are cheapest I would use them unless you have fast track or other perks with Alamo
Nick