I think the Golden Pass is one of the prettier scenic trains in Switzerland. It connects Lucerne to Interlaken, on a pretty journey over the Brünig pass that is also easily done by regular train. And it connects Interlaken to Montreux through the beautiful, authentic, and relatively little-visited Simmental valley.
The Golden Pass panoramic trains have nice big picture windows, and if you book early enough, you might even be able to book the VIP seats at the very front of the train. The Simmental valley feels like a very typical Swiss valley, with beautiful old farmhouses, rolling hills leading up to rugged peaks, and an energetic river tumbling down the middle of it all.
Unlike the Glacier Express, where you get your seat and get to keep it all day, you need to change trains quite a few times on the Golden Pass, once in Interlaken and again in Zweisimmen. I like to book the Golden Pass for travel between the Jungfrau region and Montreux – it’s a 3 hr trip from Interlaken (vs just over 2 hrs for the normal route via Bern) – but unfortunately the schedules for the train are not quite ideal. They leave Interlaken at 9 am or 1 pm, which means starting this trip from Grindelwald, Wengen or Mürren requires you to either leave quite early, or fairly late in the day. So we sometimes skip it, but it’s still a very nice trip.
You do need seat reservations for the Golden Pass, but honestly they’re not as crucial as on some of the other scenic trains. The train rarely fills up, and this is one trip where you can get on with your rail pass and pay the small additional seat reservation fee to the conductor when he comes to check your tickets. Unless you want the VIP seats, or just like to have all your t’s crossed. Then book in advance.