My 2 recent rentals in Europe:

Status: DIA

Station: VCE
Booked: the smallest with NAV (Reanult Megane) requested Diesel
Received: Alfa Romeo Giulietta

The guy at the counter said it was an upgrade form the originally booked class.
It was an okay car, no complaints.

Station: FRA
Booked: C class T model (FWMR)
Received: BMW 535XdT (LWAR ? )

Again very nice car, great foir the Autobahn. Again with "Standheizung" which is really nice in the winter. Lots of other nice features like the B&O sound system, but sadly no HUD.
240 km/h winter tyres meant that i could play on the left lane as well.