I think anywhere by train in Switzerland is heaven. Fave would be Lucerne & Geneva to Martigny
along Lac Geneve. That's 2 separate areas. Both really are beautiful and this is a grand time to see it....but I don't know when you're planning to go.
I also think that Eurail passes are such a convenience and are for First Class which is really the only way you'd want to go in Europe.
You could fly into Florence, if you can get a direct flight since the switch to train from airport is easy. Paris is treacherously (and I think disgustingly) expensive and getting to a train station from the airport will cost at least $100 if you want a taxi.
If you train from Paris, you would go through the Dijon neighbourhood. It's about 4 hours as I recall, to Geneva, but not the greatest scenery. Anywhere out of northern Italy, offers much more exciting scenery. Depending on which airport you would fly into in Milan, (you could see which offers better connections to the station) the scenery is just spectacular up into Switz.
What about training from Vienna to Geneva?