I reserve cars every month for work travel and just recently decided to give Sixt a try. All my rentals are in Dallas (Marriott). The first 2 months I reserved the BMW 2 series PCAR and received that car. Was offered a paid upgrade but declined. At the beginning of January I matched to platinum with Sixt so my first rental with platinum was middle of January:

January 2026
Platinum
Dallas (Marriott)
Reserved: BMW 2 series
Free upgrade Offered: Mercedes GLC or 3 series
Choice upgrade offered: BMW M235 for a small fee

Went ahead and went with the M235 because it wasnt much more at all ($90 or so for 4 weeks) and I was curious to try out a more performance oriented BMW. Nice car, good performance and still 30+ mpgs highway.

My next one is coming up in a few days. Will update with what it is. This thread helped me when trying to figure out if Sixt was worth a try but saw almost no data on Dallas. So far the staff at this location has been great to work with and reasonable.