Entering from Italy head for St Moritz and you have the choice of heading straight for Davos over the Fluellepass or taking the longer route south via the Julienerpass. Both are good.
Andermatt or Innertkirchen would make a good base to ride the Furka/Grimsel/Sustenen/St Gothard/Nufenen loop (It would be a crme to visit Switzerland on a bike and not do this circuit, especially Furka and Grimsel) If you ride to Andermatt on the main road from the east you will go over the Oberalp before hitting town which will be a good warmup for the roads to come.
Just north of Meringen is the Reichenbach falls made famous by Conan Doyle and worth a visit. If you head for Interlaken you are in the heart of the Berneses Oberland- big mountain territory with beautiful lakeside roads. Nearby Thun is also a pleasant town.
There are some good roads between Thun and Lake Geneva, passing close to G'Staad en route. If you follow the banks of Lake Geneva then head north towards the western end you will go through the Jura mountains on the French/Swiss border. Not as dramatic as the Alps but still some good riding and will take you close to the main routes back to the north/Calais.