I will be in Switzerland in April. Need some help in planning ground itinerary.

Some brief background:
1. I have been to CH a few times, both driving and by trains within the country. Loved it and plan to return.
2. I can fly in from DBV-GVA (or ZRH). Stay 5 nights. One hotel base for 5 nights
3. My departure flight to US is from ZRH
4. Want to do day trips by trains (and or ferries if needed) to quaint villages and some places for photography and sight-seeing as well as enjoy various forms of trains & funicular.

Questions:
Which airport should I fly into?
Where should I base, given above data
Any train pass recommendation?

Welcome all suggestions and comments. TIA!