Francs or Euro Switz

You'll need Swiss francs in Switzerland. You should find ATMs at the airport. I wouldn't go to the trouble of buying francs in advance in the US (at a not-great exchange rate), but some travelers do prefer to have a bit of local currency on hand when they land. I'd probably feel the same way if I didn't have two separate ATM cards, tied to separate accounts.

Every now and then a bank shuts down an ATM card for fear of fraud, and it's discombobulating if you have only the one card and have no local funds in your pocket. It can take a bit of time to resolve problems like that, not good if you're standing, jet-lagged, at an airport ATM. But if you had to, you could get by with just credit cards for a day or two.

I was able to use my chip credit card at both the staffed ticket office at Zurich airport and the kiosk at Bern Hbf to get train tickets.

I like having a bit of currency when I land. But if you are only going to be there overnight, use the local ATM if you really need cash.

Franks definitely. All prices will be in Franks.
There are plenty of cash machines (ATM) at Zürich airport, no need to have any Franks in advance, unless you feel more comfortable that way. Make sure your cards are authorised for use in Switzerland and Italy.

Some places do take Euros. SBB (Swiss Federal Railways) take Euros both at ticket machines and at ticket counters. The two big supermarket chains (Coop, Migros) take Euros. Some restaurants in tourist areas may take Euros, but at an inferior exchange rate (to make up for the inconvenience and extra work involved).
In all cases they will take notes only, no coins, and give you change in Swiss Franks.

Use your ATM to get a minimum of Swiss Francs once in the country but would highly recommend using your credit card. Dont get stuck with Swiss Francs in your pocket when your trip is over. All electronic purchases add a transaction fee but ask to have all charges put thru in US dollars. Most merchants oblige or have the credit card units set up for the option to select US dollars.

ask to have all charges put thru in US dollars. Most merchants oblige or have the credit card units set up for the option to select US dollars.

NO NO NO do not do that. Always put the card transaction through in the original currency. Insist on paying exactly what it says on the bill, not a Rappen/cent/penny more. This applies to both credit cards and ATM's.
When you put the transaction through in the local currency, your card issuer (Visa, Mastercard etc.) then does the currency conversion.
If you allow the merchant to do the conversion (this is called "DCC") you are giving them permission to convert at any rate they like, which will be a lot worse. Search this forum for "DCC" and you will find many posts about this. See here: https://search.ricksteves.com/?utf8=%E2%9C%93&query=DCC

Very bad advice from lvcad. NEVER allow a vendor or ATM to charge you in US dollars unless you are in the US. What you'll get is the comfort of seeing what you are spending in dollars at an extremely unfavorable exchange rate. Always, always pay or get currency at an ATM in the currency of the country. Do not take the offer to convert into US dollars. DCC (dynamic currency conversion) has been discussed extensively here and on the Internet. It is always a bad deal.

All electronic purchases add a transaction fee but ask to have all charges put thru in US dollars.

I'm sorry that is very wrong. Allowing DCC is allowing the merchant to make an extra profit on the poor traveler. Every time. VERY bad idea.

Not all electronic purchases add a transaction fee seen by the traveler.