Rental Car in Zurich - airport or city?

We fly into Zurich Saturday evenong at 5 pm and will be renting a car to drive to Interlaken area the following day

I too can't answer the main question (never rented a car in Zürich, airport or city).
Do you mean picking up the car and driving to Interlaken the following day, or picking up the car the same day you land, parking it at the hotel and driving the following day?
My answer would depend on that. I would expect the same big companies both at the airport and in the city, however where is your hotel? A hotel in the city centre is unlikely to have parking, and you may not even be able to drive to it. For a city centre hotel take the train from the airport and pick up the car in the city the following morning.
If you pick up the car the same day, do it at the airport and find a local hotel with parking.

P.S. Except, I just realised. If you are picking up the next day, make sure they are open on a Sunday.

I know I sound crazy, or maybe just ignorant, but yes, that time table is correct. We never stay in any place more than 3 days and some even only 1 day. I know that sounds crazy, and I thought it was too until we actually did it and I realized it was the perfect amount of time in most places. We don't like to lay around - we like to be active and on the go. To us, anything that is a 4 hour drive or less is a day trip. Interlaken is 1.5 hrs and Fussen is about 2 hrs and 45 mins - per Google maps. Of course, that is also the reason for the car - to give us the freedom to stay back and rest if we decide we're too tired to make the trip and need a day to just relax. Zurich would essenitially be our hub that we return to each night so we'll be flexible in our decisions.

As for where we are renting - I'm not sure. I'm afraid of the rental companies not being open early enough for us to return the car prior to our flight so it may be best that we return the car the previous evening. If that is the case, I feel maybe it would be best to rent the car in the city rather than drive to the airport, return the car, get transport back to the city and then transport back to the airport in the morning. Doesn't sound like a good plan. Of course then we also have to rely on transportation early in the morning to get to the airport in time for our flight. Plus I don't know for sure that I can return to the TO the airport or if it's a transfer thing...and if that's the case I have to add even more time into the morning. So I haven't quite figured out the best plan of action there...

We don't like to stay in hotels. We always stay in Airbnbs, so I will be selecting one with parking (no it hasn't been booked yet...I know that needs to happen soon! We just booked our flight though so I haven't gotten that far yet)

I didn't realise you were planning to stay in Zürich and do Interlaken and Füssen as day trips!
To each their own.

• There is a hotel at Zürich airport, walking distance to the terminal, but it ain't cheap: https://www.radissonblu.com/en/hotel-zurichairport
• For your Interlaken excursion, make your destination Lauterbrunnen (end of the valley). Route here (1h56 + stops): click here for route on Via Michelin The suggested route via Luzern is best, as it takes the scenic Brünig pass route.
• Zürich to Füssen is 2h45 + stops. Route here: https://www.viamichelin.com/web/Routes?departure=unique%20zurich%20airport%2C%20Kloten%2C%20Switzerland&arrival=87629%20F%C3%BCssen%2C%20Germany And you will need to buy an Austrian Autobahn Vignette.

Scythian, I agree. I am currently organising a trip for first week in April. Nothing booked so far. I am still trying to decide whether to fly or train - or possibly fly there and train back, stopping off half way.

First of all - I have NO idea how to reply to a specific post so sorry for this jumbled response to all:

@Chris F. - thank you!! That is wonderful information! I will absolutely check those out!

@Scythian - I have heard that to be true lol Last time we were in Europe we spent some time in London. I had booked the flight about 6 months in advance on a good deal for the flight and then searched places to stay. By the time I had decided to book, the place I wanted to stay was unavailable. I found that about 95% of the places I had picked out were booked for my dates. I had to settle on a poor quality and yet expensive stay. And this was about 5 months prior to our travel date! So I guess I've been burned by waiting too long :-) We're also going to Greece and most of the places I had selected to look into are no longer available for the dates I'm looking at.

Oh my gosh...didn’t realize from your initial post that you’re actually basing yourself on Zurich each night and getting up every day to drive someplace. You say you like to be active, but it seems most of your activity will be in the seat of car. Interlaken area (not interlaken town) is one of the most beautiful places in the world. You’ll be short changing yourself by not spending the night there.

Tim I know... I'm actually kind of sad about only one day in the Interlaken area. I had originally planned 2 days in the area but our finally itinerary is only allowing for one if we still want to go back to Fussen area. (I was sick last time and only able to hike a little so we want to go back there to actually hike the mountains by the castle). We loved Prague and Dubrovnik so much we're going back there as well so we definitely revisit places we like. But the first time around we regretted our short stay in Prague... I feel it may be the same with Interlaken area.

Have you been to the Fussen area? Would you say 2 days in Interlaken is worth skipping Fussen for? With the car rental we won't HAVE to go to Fussen so it's still up in the air for debate...

I've been to Fussen and Murren/Wengen/Lauterbrunnen more times than I can count. I would never trade away my time in the Berner Oberland for time in Fussen. Yes, Fussen is a nice place, but it's nothing like the BO.

We drove from St Gallen to Fussen, and it took at least 2 hours each way. Zurich is quite far from St Gallen. When are you going to have time to backpack?

We rented a car from the Zurich airport and didn't have problems.

If we left at 7 am, arrived by 9 or 10 and headed back at 6 pm - Even then that gives us 8-9 hours to hike...though I doubt we would hike that long. Maybe 5 hours at the most.
Is that not realistic? Where we live now we have to drive at least 2-4 hours for any good mountain hikes and we do that quite often, so it's seems realistic to me to do the same there.

Jamie, if you are regular hikers, you will be familiar with topographical maps. Swiss topo maps are available online.
This link takes you direct to Lauterbrunnen area: https://map.schweizmobil.ch/?lang=en&bgLayer=pk&logo=yes&season=summer&resolution=5&E=2636791&N=1160246&layers=Wanderland

Green are signed footpaths. Dashed green is mountain tracks - more difficult.
Red is railways and cable cars (also called railways in German)
Map squares are 1 Km.
Valley runs north - south. Road (yellow) comes in from Interlaken from the north, and ends at Lauterbrunnen. Steep cliffs left and right at the sides of the valley, up to the mountain tops.

You can zoom and pan as you wish, and print out (PDF file) at your desired scale (1:20,000 1:25,000 1:50:000 etc.)

Enjoy.

Agree with Tim. I wouldn't bother with Füssen at all. Spend that time in the Lauterbrunnen Valley. You can take the train there directly from the airport and be ready to hike the next morning and return on the train to the airport. No car needed.