Not sure how this thread got started again as it appears to not be recent but:
Ive never rented in MIA but have returned here plenty of times. One of those times I even hung out for a bit in the general Hertz customer area while waiting to be picked up by a livery service.
The general line appeared to be very long at time. I took a bit of time looking at their car selection and most appeared clean enough for me (I'm very picky about clean cars) and well maintained in their Gold area. The Gold hut also seemed to have little to no wait for customer questions or problems while I was there.
I have never had a problem returning a car here.