Visiting Switzerland for the first time.

Hello Pradeepto, and welcome to the forum! The Swiss Saver Flexi Pass may be a good option. One disadvantage is, however, that it's only valid between your first and last free travel day. The most logical first free travel day would be the transfer from Zurich to Interlaken. This would mean that you can't profit from any discounts while you're in Zurich. An 8 day Swiss Saver Pass has a similar disadvantage: it can't cover all ten days of your stay, so you should choose to not to use it during your first days in Zurich. This doesn't have to be a problem if you plan to stay within or near Zurich and to make not to make any long trips. A 15 day Swiss Saver Pass will offer free traveling (in cities as well) during all days of your stay, but this may not be the most economical solution.

As for the Swiss Flexi Pass: you can choose for yourself which days you want to count as free travel days and which days as discounted days. On free travel days, unlimited traveling in regular trains, buses and boats and in public transportation in major cities applies. On all days in between the first and last free travel day, a 50% discount applies. Cable cars and mountain trains are discounted, both on free travel days and on the remaining discounted days. The Gornergrat (if that's where you want to see the Matterhorn from) is discounted by 50%, the Jungfrau by 25%. So it's up to you to decide which plans you have for a specific day, and then choose whether you want to use one of your free travel days or profit from discounted traveling. Please take a look at the maps showing the areas of validity of both passes. Links to those maps can be found under the header 'Features' on the Swiss Flexi Pass and Swiss Pass pages.

The timetable will help you do the planning for your Jungfraujoch trip. You can hike small parts of the route, but only up to Kleine Scheidegg. It's easiest to make the entire journey by train. Up from Wengen/Grindelwald, a 25% discount applies with both a Swiss Flexi Pass (whether it's a free travel day or not) and a Swiss Pass. If you're coming from Interlaken, it may not be worth using a free travel day for that trip (as free traveling only applies up to Wengen/Grindelwald).

I'm not sure about the Street Parade. The city will be very crowded. That's no problem if you like such festivities of course, but if you want to explore the city in a more relaxed way, you may indeed reverse your itinerary.