When I was working and living in Miami Florida my boss sent me to Auto Boutique Car Rental in Miami.
The car I picked up for my rental was a nice Luxury Car and I wish I could afford to own one and hated to give it back.
I miss working for the company who used to rent me Luxury cars to drive but the business went out of business so I had to find another job.
I'm sure there's other car rental companies in Miami Florida for Luxury Cars but that was the one I had experience with and they were great with their customer service as well.
Here's the link to their website.