Renting car in Austria

Have anyone been renting car when traveling in Austria and has any suggestions on the car rental provider? I was looking at Hertz, Europcar and Sixt as they are bigger companies and thought might be more trusted.. though I see there is quite few car rentals like U-Save or Mega Rive which I never heard about, but are half cheaper. Which is tempting, but also concerning if they won't tey to be dodgy. Any recommendations would be appreciated!