<<". We have also heard that it's possible to take the Golden Pass on part of this route, but it's confusing us whether we should take multiple local trains, the Golden Pass, or if it's the same route. ">>
High Andy Jen -
The Golden Pass train uses the same tracks as all the other trains on that (those) routes. But, you don't have to change trains, as you would otherwise.
You do have to get from Wengen to IO via Lauterbrunnen to pick up the Golden Pass route, or any other of the routes i mention.
That is why I suggested the SBB web site as a reference. It can help you decipher the routes, especially using the map option.
If you do not purchase the Golden Pass ticket, you can use local or long distance trains over the same tracks, and make your own timetable. However, the Golden Pass trains have special scenic cars with extensive glazing, well up into the roof, IIRC. Great for views and for sunshine. They also used to have inadequate air conditioning for sunny days in that type of car, and the windows did not open. So, when I travel those routes, which I have not done for 5 or 6 years, I avoided the panoramic cars. To each his own. And, they may well have improved the air conditioning. The moderators may know about that.
It is nice to stay on one train, without the need to transfer luggage when you change trains. That is a benefit of the Golden Pass ( or other such named routes.)
I have always found the descent into Montreux through the vineyards (which is on the Golden Pass route) to be one of the most beautiful short stretches of rail travel in all of Switzerland. The Golden Pass route passes through Zweisimmen between Spiez and Montreux. You can force the SBB computer to select that route if you put in Zweisimmen in the "via" box. The whole ride is quite scenic, but, for me, that section coming down to Montreux is the best part.
The travel time (IO to Montreux) is one the order of 3 hours to 3 hours 10 minutes.
Caveat Emptor- currently, there is extensive construction on the last part of the route, and the line is closed some days in April. It looks like it will be finished before May. Might check with the SBB, or at least look at the timetable on-line.
If you do not put in an intermediate stop in the "via" box, the SBB timetable chooses the route through the new Lötschberg tunnel as the fastest route to go from IO (Interlaken Ost) to Spiez, to Visp (near Brig) and along the Rhone Valley to Montreux. That route has its own attractions, but the long tunnel section means that you miss some of them. It takes about 2 hours and 10-20 minutes.
If you want a really special train ride, you could pick up the Lötschberger in Spiez, travel via Kandersteg, and down the BLS Südrampe line to Brig or Visp, then catch the train to Montreux. I plan to walk the rail trail along the Südrampe in June with my grandson. Time on train- 3 hours 20 minutes. About the same as the Golden Pass through Zweisimmen, but withsome changes of train.
Also, search BLS Südrampe wih Google
It use the old higher route route (force the choice with "Kandersteg" in the "via" box on the SBB web site) with a much shorter older tunnel, and a fantastic ride down the wall of the Rhone Valley
Finally, there is a northern route. If you choose to take local and long distance trains via that geographically longer route from Spiez to Bern, where you would change trains, then from Bern to Montreux via Lausanne, it takes less time in the train (2 hours and 35 to 40 minutes), and, you could, if you chose to, get off in Bern, put your luggage in a coin locker or the left luggage office, walk through the very nice old town to the Nydeggbrücke and up the hill to the Rosegarden, and return by walking back down to the Nydegg Brücke and catching the tram back to the Hauptbahnhof.
I've spent time in Montreux on vacation and also at business meetings. I'd rather look at Bern, and it is easier to walk around. The lakefront promenade at Montreux is very nice, however. So is the cograil ride up to Glion and Caux, and all the way to Rochers de Naye.
<<". So is this golden pass best route by rail the best one?">>
As you can see from my extensive comment, I don't think so. However, you and I are not the same people. "Best" is a word that has to be judged from the eyes of the beholder, not from the eyes of an advice giver with different perspectives and level of experience. I value flexibility over convenience, and often take routes where I change trains. If you have heavy luggage, that is a problem.
I have used the various luggage transport services. Years ago you could check your luggage onto the same train youe were taking. Now, the fastest service (same day) is available only at selected stations:
Wengen to Montreux is listed as available for Fast Luggage.
If you are going to stay at the same place for a few days, the slower service might work. Or, you might send some ahead for pick up part way through a circuitous route if you want it waiting for you when you pick up a rental car.
Personally, unless my time in Montreux were critical, I'd take the BLS Südrampe route via Kandersteg, or the northern route through Bern. But, i know the routes, and don't mind transferring luggage. "Travel Light," as they say. Or, send your luggage by Fast Luggage.
Hope I have not confused you. You need top look carefully at a map.
A good one, which gives train stop information is at MapSearch.CH
Select Map/Route tab. I find the Classic interface ( box at lower right corner of home page) to be easier for me to use.
Planning a trip is the sometimes the best part....especially if the weather does not cooperate. Switzerland has extensive resources to do such planning, should you care to use them.