what kind of lift pass to buy for Berner Oberland, etc.

If you search this Forum using the search box above or just scrolling through a couple of pages, you will see this has been discussed many times and several times lately. I think the extensive discussions that have happened so far will provide you good information and help you decide.

I would discourage renting a car as Switzerland has the best public transportation. A car is absolutely not allowed in Muerren. You'd have to park it in Lauterbrunnen.

In September 2014, I did the same trip in reverse (3 nights in Luzern, 4 nights in Mürren, and 3 nights in Lausanne). You definitely don't need a car for this; the trains work great.

Since I was taking trains everywhere and wanted to go into some museums, I got a 15 day Swiss Pass. It worked well, but I had figured out which trains I was definitely taking and their cost, and which museums I was definitely seeing, so I knew it would pay off. Doing this is the only way to know (many talk of making spreadsheets; I just added it up on a piece of paper). When researching costs, be sure you're looking at full price tickets; the first price shown on the Swiss transit site http://www.sbb.ch/en/home.html is half price, as Swiss people all get annual half price cards.

Of course, since I went they changed the rules and terms for the passes, so even if I took the identical trip again, I'd have to re-do the numbers!

If you're not sure what the best deal is, it's hard to go wrong with a half fare card. It cost 120 CHF, and is good for everything that moves in the entire country, from local buses all the way up to the very expensive Jungfraujoch trip. As long as you're taking more than 240 CHF of rides, you can't lose. And this is particularly true if you're taking Jungfraujoch roundtrip from Mürren. The current full price for that is 205.60 CHF; add that to your Lausanne to Mürren and Mürren to Luzern rides, and the half fare card is already a deal.

The other factor to consider, however, is convenience. With a half fare card, you have to buy a ticket every time, before you get on a bus, train, boat, tram, etc. (if buying out of a machine, select the half fare option). With a Swiss Pass, you only have to buy tickets for things not fully covered; for everything else, you just flash your pass. I enjoyed this "luxury," so if the price is close, consider getting the pass for the convenience.

If you are driving, you may want a pass just for the Berner Oberland.

It sounds like you are talking about the LIFTS, right? Cablecars, gondolas, etc.?

...or are you talking about trains?