Still tweaking that itinerary and wanted to break this question out into a separate post. We will be In Switzerland in September and are currently considering taking boats on all four lakes (just the Lausanne/Vevey/ Montreux area of Lac Leman) but since we are trying to make things less rushed, we wonder if this is overkill. Of the four, which do you most highly recommend for scenery and for towns to visit (such as Oberhofen and Hilterfingen on Lake Thun). And since we wouldn't have to do the entire lake tour, which are the most beautiful segments?
Thanks in advance for your suggestions!

We spent a wonderful day driving around Lake Brienz, stopping for lunch an sd shopping in different towns.

We spent 8 wonderful days in a chalet in Brienz, I thought the Lake was so beautiful. Also close by is the Ballenberg Outdoor Museum and the Brienz Rothorn Bahn www.brienz-rothorn-bahn.ch/en.html
The lake has the BO mountains as a backdrop - just stunning.

We also stayed in Vevey and loved our ferry ride back from Lausanne, the buildings and vineyard terracing were amazing. We also enjoyed an afternoon wander through Thun and a walk up to the castle. Such a beautiful country - wish I was back there now!

If I had to choose just two it would be Lake Lucerne and Lac Leman [the Eastern part as you suggested]. That would give you a taste of German-speaking and French-speaking Switzerland. Lake Brienz is beautiful too for its colour and natural scenery. If you're able to see the whole of Lake Lucerne, ie the southern end as well as the built up end you'll see beautiful scenery there too. Lake Thun would probably be #4 on my list, but I would happily do boat trips on all four. I have only seen Lake Brienz and Lake Thun from trains [apart from waiting for over half an hour beside Lake Brienz for a boat that wasn't coming, because the season had finished the day before - it was October!] I don't think it's overkill if you find boats relaxing. I've had three trips to Switzerland over the years and have always included a few boat trips, as well as much train travel around lakes.

Thanks for sharing your experiences. We do find the boats relaxing but hope not to just see the same scenery over and over again. It's so difficult to make the hard choices required by a short trip!