One night to spend in vicinity of Lucerne

beverly,

Lucerne would be a great choice! It's a beautiful city with lots to see, and it's an easy trip from there to the Zürich airport.

Seconded. Stay IN Luzern for your last night, not near Luzern. Lovely city, and if you are in the centre you will be walking distance form the station, and it is only 70 minutes from the station to Zürich airport.

Do you need a third on Lucerne?! It's stunning. Since you will have been in Murren which beats Thun or Brienz in my opinion, you should do Lucerne. You will wish you had more time there and will probably want to go back! If you are planning to stay in Zurich before flying out, consider spending that night in Lucerne as well, its about an hour to Zurich airport, I believe.

Neither Brienz nor Thun are especially convenient to Zurich airport. It isn't clear from your profile what country you are from but if it an intercontinental flight home then you need to be at the airport 3 hours ahead. That's 1:30, right?

If you are at the mercy of possible missed connections on the trains, either because it is a tight connection or the train is rerouted on a Sunday for planned engineering works, you need to leave plenty of wiggle room so you are not stressed out by worry.

A simple connection like Luzern - and all its fabulous beauty - will work much easier.

Brienz you are adding 90 minutes plus a connection to the already hour from Luzern. Very scenic 90 minutes, but still....

Thun will have a short commuter train into Bern, change to Zurich, and possibly change again for the airport.

If you haven't been to Luzern you won't know what you are missing....

Thank you all for your comments. Lucerne it will be!!