Plus you avoid the regular city hassles of Zurich. Smaller is better in Switzerland.
We stayed in Interlaken. It was nice as there were a ton of options for travel, by train, car, and boat. We loved boating to Thun, driving to Lauterbrunnen, training to Luzern.
But staying in Luzern gives you a bit more easy access to the eastern side sites. If I had to do it again, I would pick Luzern for a base (but we only spend a few hours in Bern, so don't have a strong opinion either way on it)