The GoldenPass Panoramic train travels between Montreux and Zweisimmen in the Gstaad-Simmental region.
In Zweisimmen, you can change trains and continue directly to Bern (with brief stops at Spiez and Thun on the way). So if you are staying in any of these places, the Panoramic options is better than the GoldenPass Express that goes directly to Interlaken.
The Panoramic train is also a good choice if you are visiting the Gstaad region. It has a more frequent schedule than the Express and is easier to get a seat reservation.
Reserve seats for Panoramic train here. Tickets are free with Swiss Travel Pass.