We had a great experience with Sixt at Tocumen and would recommend. Specifically, staff at the check-in desk was really informative and helpful, and gave us great tips for our trip.
I appreciated that Sixt includes the insurance in the price and that pricing felt very transparent overall. The contract does mention the large deposit but that should be more clear; it seemed to be the biggest complaint in other reviews.
Overall, we had great service and felt we got a good price for the rental. I would definitely recommend and use Sixt again.