We are planning 6 nights in Switzerland. Flying into Zurich, we plan to take the train to Berner Oberland for 3 nights. Then move to Lausanne for 3 nights, before moving on to Italy. Are we making a mistake by going to Lausanne rather than stopping in Lucerne for 3 nights?
Yes you are; I liked Luzern better.
I also prefer Lucerne to Lausanne. That's not to say that Lausanne doesn't have it's "charms" but for me there's something special about Lucerne, and some nice day trips possible from there.
Regardless of which place you choose, be sure to pack lots of money as Switzerland is expensive!
They are both worthwhile, but the areas are different. I would recommend Vevey over Lausanne. I like Lucerne, but I love coming home to the Canton of Vaud. I never tire of walking the Unesco Lavaux vineyards which bring you through some very charming villages with breathtaking views. No matter where you travel in Swiss, consider taking in some local festivals.
Here's a link for the local tourism site: