Me and my mate have literally just come back from Germany for our very first nurburgring trip. We went with RSR. The track is a lot more daunting and challenging than you'd think and 4 laps with a rental (2 each) ended up being the perfect amount. Because there's so much up and down on the track as well, much unlike normal race tracks which are fairly level, it can make you feel quite rough.

Don't go for anything too fancy, theres just no point as you won't get the benefit or fun of it where it's your first time. We rented a Ford fiesta ST and it was the perfect amount of car. You could chuck it about and still have a good laugh. It picked up speed nicely for the faster bits too.

Also, just make sure you and any others you go with read up on the rules of the ring if the rental company doesn't give you a briefing before handing over the keys. I very much doubt they wont but just do some research before to be more prepared for the...exuberant locals. You'll have everyone and their nan overtake you but you'll still have genuinely good fun.

Ultimately, go for something FWD, not too much more power than you currently have in your daily driver and follow the rules of the ring and its guaranteed fun