I've never rented from Thrifty so I can give any info about them. We've rented from Dollar in TPA and they were fine. Both companies are in-terminal so that's not an issue.
Join Thrify's "Blue Chip" club and then get your ressie linked. I've had good luck with Thrify but never used Dollar.
Keep pricing the car, it might get cheaper.
I've used Dollar in TPA a couple times and had no problem with them. Nice, clean cars both times AND they're on-site, not like National, where you'd have to take a shuttle.