What is the best travel ticket for travelling around Switzerland?

SBB offers a Swiss Travel Pass which might suit your needs

With the "Swiss Travel Pass 15 days" you can enjoy 15 consecutive days of unlimited travel on the entire train, postbus and boat network of the Swiss Travel System.

So basically you can use more or less any public transport (also in cities) with this pass, including some mountain railways and a lot of museums. Besides the 8 or 15 days option there is also a more flexible version (Swiss Travel Pass Flex) which allows to travel on 8 or 15 days within a month.

You can actually buy the pass already in advance and print it at home, so you won't need to worry about getting it once you've arrived.

Only constraint is "vailable to persons permanently resident outside Switzerland and the Principality of Liechtenstein"

It really depends on your individual travel plans though, so it might be cheaper to get individual tickets instead (or a Flex Pass for just the few days where you intend to travel a lot). If you already know where you want to go to you can use the timetable information on sbb.ch to learn about the cost of the individual tickets.

In that scenario you also need to consider the price for the pass for the trams, trains and busses within the city of Zurich (CHF 85 for a monthly pass, about 50 for six day passes).

As an intermediate between the Swiss Travel Pass that nohillside mentioned, and buying full fare individual tickets, consider the Swiss Half Fare Card. Valid for one month, and for CHF 120 you get 50% discount on all public transport including many mountain lifts. Look up the fares of train journeys you might take at https://www.sbb.ch/, with or without the discount, and calculate if it's worth it for you. I'd reckon it probably is, in particular if you plan on taking mountain lifts, where the Swiss Travel Pass discount may be no more than the Swiss Half Fare Card discount.

If you'll be spending all or most of your time in or along two cities, another possibility (though not specifically aimed at tourists) is the Point-to-Point card, which is a weekly/monthly/yearly pass for just a particular stretch between two cities. It also includes some travel on public transit in each of these cities; you'll need to find out the details for the cities you're considering.

My wife and I purchased these for the Bern-Fribourg route during a 15-day trip where we stayed in a city along the route. I think the price at the time averaged to about 15 CHF per person per day, and we avoided the hassle of buying train tickets; we could just hop on any train and go to Bern, Fribourg, or anywhere in between. In Bern and Fribourg, any form of public transit was included in the ticket.