Depends really, I like Chur but that may a bit too big for a typical Swiss town.

Although it get's overrun with tourists I think Altdorf retains a certain Swiss feel, it is very much a working town but with lots to do. You could easily fill a day out here and it's only about 90mins via train and bus from Zurich. Typical Itinerary for Altdorf and surrounds, get the bus to Burglen, another 15 mins past Altdorf. Get off at the Tell Museum (I mean depart the bus not enjoy it in an excessive way). You could easily spend an hour there, then walk back to Altdorf through the country paths that have around 10 stopping points en-route that tell the story of Willian Tell and Swiss folklore in nice bitesize chunks. Then go for lunch at one of the many restaurants (though my fave is Nussbaumli on the mountainside). Have a nice relaxing walk around the town for an hour or so. With the space you left after lunch enjoy a lovely afternoon tea/coffee and a cake at Danioths, have a look at Telldenkmal. Bus back to Fluelen (or walk the mountain path behind the town takes about 30 mins to Fluelen) have a couple of hours in Fluelen by the quayside, see the Gotthard crystals in the church, if the exhibition is still on, then catch a paddle steamer to Brunnen. Walk through Brunnen to the station and hey presto you are back on your way to Zurich!

As an alternative there are some lovely walks from the top of the Eggberge cable car station between Altdorf and Fluelen if the William Tell trail aint your thing.

(I should work for the bloody tourist board!)