We were supposed to be heading to Switzerland this week for a 2 week group tour - now resked for next year - so have done a lot of reading. Our tour starts in Lausanne and ends in Lucerne. We had planned extra days in Lausanne and Zurich.
Main things I found to do in Lausanne: Chateau de Chillon, the Olympics museum, lake cruises, the chocolate train (one day tour from Montreux to Gruyere), a nice old town area with cathedral and some interesting art galleries (Collection de l'Art Brut which RS tours in one of his videos). There is also a wine region just east of the city. Lausanne is one of those Swiss towns that if you are checked into a hotel there, they give you a free transport pass for the local metro and some discounts at some sights. Here's a link I've found useful from their tourism office https://www.lausanne-tourisme.ch/en/lausanne-transport-card-and-more/
Everyone says Zurich is kind of boring and mostly business like. However, there are day trips you can take from there, there is the National Museum, short river and longer lake cruises, other museums, etc. We had planned 3 nights there including a day trip up north to the Rhine Falls area and I found enough to interest us. Advantage to it is good connections for flying out of Zurich and it's pretty easy to get to the airport from downtown i.e. the area near the main train station. I think Lausanne is probably more of a laid back scenic town vs Zurich.