Due to a long relationship and good prices and service in the USA, I always rent from Avis. That may not always be the most economical way to go, but that is not an issue for me. At least twice it has gotten me a car when none were available to my traveling companion and we needed to rent on short notice. And, when I used to travel frequently on business, they always found me a car, even when none were officially available.
Recently, when I have rented at the Avis Gartenhofstrasse location in Zürich, I have been able to return the car at off-hours. They have added a key-drop. i have not asked if it could be used with cars rented elsewhere, but it is not obvious how to do it, and I needed an explanation from the clerk.
I never rent at the Zürich airport, because there is a tax or fee that adds 10 % ( I recal) to the total cost of the rental at airports. Return to the airport does not have that fee.
And, each time I have checked rates in Switzerland, there is a "hidden" drop - off fee, if I return a car to a location different from where I rented it. It shows up as a higher per day rental cost.
My travel pattern is to use public transport on the first and last few days of a trip when I am staying in Zürich. In the days in between, I use a mix. perhaps I'll leave the car at my inn or at a bus or train stop convenient for a hiking trail, then use public transport to complete the circuit after I hike.
Or, if I go to visit in a city, I always take a train. Finally, the Swiss law is quite strict about driving with even a very low blood alcohol content, so if I indulge in wine at a meal, I don't drive afterward. There is sufficiently frequent public transport to make this easy. For example, many times I have joined a friend for dinner in Luzern while staying in Zürich, or vice versa.