We plan to spend our 9 days switerland trip at Wengen or Murren and Luzern. Should we stay at Luzern for 2 nights and 6 nights at Wengen or should just base at Wengen(8 night) and go to Luzern when weather is not good? Please advise.

If I wanted to go to Luzern for two days, which it seems you do want to do, I wouldn't base in Murren or Wengen. It is at least around 2 hours travel time each way. I can appreciate your desire to use the best weather in the Alps. The weather can be so unpredictable there and can change in a hurry, and views depend on it. I would think with 6 days in Wengen, you would be likely to get at least some good weather (no guarantee of course). If you end up with the best weather for Luzern, that is not such a bad thing. Use some of the good weather to go up Mt. Pilatus or to take a cruise on the lake.

You did not say what time of year you will be there. It makes a little difference, but I am not sure just how much.

Being in Wengen, or Mürren, loses some of its charm rather quickly when the weather is dreary, and it frequently is. I am not trying to sound pessimistic, but those are the facts. There is always that risk. I would think in terms of using Bern, Thun, Spiez, and Luzern as back up visits for the cloudy days.

When I go there, I usually plan on a week or more in Lauterbrunnen, which is a little easier to get in and out of because cars are permitted. The train schedules up the mountain to either Mürren or Wengen from Lauterbrunnen are coordinated fairly well. The whole timing depends on the BOB train schedules from Interlaken Ost to Lauterbrunnen.

If you are staying in Mürren or Wengen, I presume you will not have a car to use. (Neither town permits private vehicles to my knowledge. I find that if I have one the whole time, it often sits "deadhead" for a day or more next to the apartment at the same daily rental cost as if I were using it.)

The availability of a car becomes a factor because the train schedule between Luzern and either Wengen or Mürren is not very favorable.

You can leave Wengen at 5:43 and get to Luzern at 9:03 with changes in Lauterbrunnen and Interlaken Ost and Bern. (A relatively circular route.)

Or you can leave 2 hours later at 7:43 and arrive at 10:24 with 2 changes: Lauterbrunnen and Interlaken Ost. There are other connections that get you in at 11:24 and 12:24. (That late, and the day is starting to shorten.)

Coming back, there are two good late afternoon connections. One leaves at 18:34 and one at 19:34. You return to Wengen at either 21:14 or 22:14.

The last train back returns at 23:14.

The train connections are slow because the trains don't go very fast and they make a lot of stops. For example, the so called "Schnellzug" from Interlaken to Luzern stops about 10 times. Some of then even more.

I drove from Lauterbrunnen all the way to the Luzern transportation museum in about an hour and 10 minutes less than the train takes.

When you consider that we could leave when we wanted to, we got to Luzern much earlier than the train, and the trip took us more than an hour less on the clock. We drove back about an hour faster than the train schedule as well. So we had 2 hours more to look around.

The problem is that renting a car is expensive, but so is train travel without a discount.

The train fare to Luzern for 2 people will be more than 200 chf undiscounted. That is about $160. You can rent a car more cheaply. Swiss trains are not cheap.

There is an office of Europcar within walking distance of Interlaken Ost.
Coming out of the train station, look to your left and the office is about 500 yards away. The Avis office is closer to Interlaken West. I found that the car rental offices tend to keep bankers' hours.

Well those are my views on the question. I am sure you will get different opinions.

Thank you for the info. We will be there June 26- July 5 and yes, we do not have a car. We would prefer to use public transportation. Do you recommand other place instead of Luzern? We have been to Luzern once for few hour and have been Zermatt for 2 days and loved it during our last trip(10 years ago). Is it a good idea to take part of Glacier Express to Zermatt instead of spend 2 days at Luzern? Any suggestion will be welcomed. So far, we only decided the Jungfrau Region for at least 5 days and open for other days.

I don't know the answer about the Glacier Express because I never rode on it. I rented a car and drove over the mountain passes and that was something of an adventure. We could stop often and look, and take short walks.
The Glacier Express is not between the Berner Oberland and Zermatt.
The one I am thinking of goes to St. Moritz. It is a winding route through the valleys and a few tunnels.

The last time I was in Zermatt, we drove from Lauterbrunnen by way of the Lötschenberg tunnel between Kandersteg and Goppenstein. It is a fairly easy drive and we made it down and back in a long day that was very interesting.
I think it took us about 3 hours to get to Zermatt and 3 hours back. We had time in Zermatt to ride the Gornergrat train to the end station and look at Monte Rosa and the Matterhorn as long as we wanted.

It is a tough question to answer because we cannot predict the weather. If the Berner Oberland is socked in, Zermatt probably is too. Although there is no assurance that is the case.

The way I look at it is that if I am in one of the mountain villages first, and the day is cloudy, I can go elsewhere for a visit. Thun and Spiez are neat towns.
So is Meiringen.

A car can be a cheaper means of transportation if there are 3 or 4 people riding in it relative to buying undiscounted train tickets.

I rented one last summer, but it turned out to be darned expensive.
Not sure what I will do this year in September.

Personally, I'd split up the time in two different places to avoid travel time.

If it's alpine areas you're interested in, you might consider a stay in Engelberg as well, which is only an hour from Luzern by train.

Good morning would personally take Luzern as one base as from there you
can take water transportatiion to Vitznau (Rigi) and Alpnachstad (Pilatus). And rail to Engelberg (Titlis) and also rail to Alpnachstad.
Pilatus also can be reached thru Kreins
by local bus.... You also have access to the entire Lake Lucerne, in fact when the weather is bad in the mountains you can take a lake steamer and spend as much time around the lake such as Weggis, Fruelen, etc...
For the Berner Oberland would pick Lauterbrunnen or Grindelwald as a base
both are at the end of rail from Interlaken Ost. The inclinde railway and surface rail to Murren. The WAB
up to ?Wengen and Kleine Schedigg and
onto the Jungfrau. From Grindelwald you have the WAB taking a different route too Kleine Schedigg.. From Grindelwald the chair lift up to Grindelwald First. The chair lift from
Grindelwald to the Mannlichen and then
by cable car down to Wengen or walking to Kleine Schedigg. If the weeather is adverse wouold suggest returning to
Interlaken Ost and there behind the station is the boat docks for Lake Brienz, Brienz and Ballenberg are intersting places. Then from Interlaken West. (a short ride from OST) you have the boat docks for Lake Thun., Spiez, Thun and the castle at
Oberhofen again are worth a visit. You can spend much time in the BO..
Do your research on both areas to make sure you get to see most of what you
want to see.. Richard of LaGrange Park, Il..

Two years ago, we stayed in Wengen (in a self-catering apartment) for 6 nights and trained to Luzern for 2 nights. We did not have a car and we were able to see all the places we WANTED to see e.g. Jungfraujoch, Schiltorn, Murren, Lauterbrunnen, Grindelwald etc.I think it was just the right number of days to get the flavor of the Berner Oberland.

Sorry, hit the "post reply" button too quickly. After the 6th night, we took the train to Luzern arriving before noon. The 2 nights we spent there was again just the right time for us to enable us to see the sights of the city including a short trip to Mt. Pilatus and a boat ride across the lake.