Among the issues are whether you want to imagine you have the absolutely lowest possible rental price, whether you need an automatic transmission without-fail, and whether you are concerned with substitution of the reserved vehicle. Another issue might be ease of using your Credit Card damage-waiver, if that is important. Auto rental rates are way up right now, so there will be price shock in any case. It's not a simple matter to select a company. My experience at FRA (Frankfurt) may not translate to Dresden, but I found that the big rental companies had lines at their desks and had to wait for cars to come in and be turned-around for rental. I reserved an automatic, but they offered me a massive van that I didn't want. I asked for a smaller standard-transmission, and even that took almost an hour to come up with.
I personally consider it wiser to rent directly from a big company website, rather than using an aggregator or re-seller. But that sense of safety may be an illusion. Last summer in Charlotte, NC, I had to wait in a hot line for an hour, when my Avis membership was supposed to get me a car waiting in a space with no desk visit. (Yes, that's the USA.) It's also important to check carefully for branch office hours, including lunch hours if mentioned.
With five passengers, many European car models may be cramped for Americans (possibly) used to Chevy Suburban or similar vehicle. But you don't want a big vehicle in civic parking garages, or on one-lane medieval city streets. Historically, I've had trouble with luggage fitting under the supposed luggage-cover in hatchbacks. One time, the luggage cover was missing (and noted, on the rental contract.) And that's just for two people.
