@jamesjefferies Definitely from Martigny up to the Vallorcine. In my book the most impressive railway in all of Switzerland. There are a few more quite steep lines in that area out of Aigle and Bex.
The best bit of the MOB is the climb out of Montreux – you can turn that into a loop Montreux – Montbovon – Romont – Lausanne.
And then there’s Jura. Neuchâtel to La-Chaux-de-Fonds is pretty cool, from there onwards on the narrow gauge to Le Noirmont and either Glovelier or Tavannes.