I had the worst experience with Sixt among all Armenian rentals.
First of all, they completely disregarded the booking options including permit for crossing the border and additional driver and we had to delay the trip start for a few hours.
The car (7 seat SUV) had problems with transmission, winter tires, parking camera was blurry to the point it couldn't be used and the stuff couldn't answer most technical questions.
I got a small dent in the front bumper and they asked ~250$ fee for the damage although the stuff didn't even notice in until I've explicitly shown them.
This is some fraud-level prices given the fact the car was returned 1.5 days before the deadline, the car and especially the front bumper were in heavily used condition.
Arguably the best car rental in the city, all things considered. Not the cheapest, but with reasonable prices (a bit greedy on the extras, though), with convenient user interface. Could use round-the-clock pick-up and return in downtown.