I've rented with Avis, Hertz and National for the past 30 years as I traveled a lot for business before retiring last year. The point programs always worked well to get free rentals when I traveled for personal use. This has been one of the perks that I have started to miss this year, beside the Hilton Honors points. The first trip we made this year completely on our own dime we tried a discount rental through Amex Travel.
We had a terrible experience with Sixt in Ireland. I booked them through Amex travel and when we arrived in Dublin they tried to deny acceptance of my rental coverage through Amex. They kept insisting on a 580 Euro insurance coverage for the week. Once I got Amex on the phone, they insisted that a copy of the coverage be faxed to their location before they would accept it. Once the fax arrived the 580 Euro coverage became a damage waiver required in case my CC insurance didn't cover the damages. Then to top it off, they required another 200 Euro just to allow my spouse to drive since it was my CC and they would not cover her since her name was not on the card. It took us 2 hours to get through the hassle just to get our car. After we returned it we still had to fight for the "deposit" because they claimed we had photo radar tickets but could somehow they could not produce any record of the tickets. 4 months of fighting just to get our deposit back.
After our trip I watched an "expose" show that looked at almost all of the rental companies at airports in Ireland and most of them were doing similar tactics to jack the rental price because they made commissions on the add on sales. Sixt was the worst of them all as the location managers, according to x-employee testimonials, forced the staff to attend training on how to jack the add ons. Tons of complaints about this on TripAdvisor as well. I guess I should have read that before I went.
I've spoken with people outside of Ireland who have not had anything near as bad with Sixt but the experience in Ireland will keep me from ever renting with them again.