Due to great airfare sale, we are flying to Paris in late August, then going to Switzerland for the bulk of our trip, before returning to Paris via Lyon. We have these train trips to figure in: Paris to Interlaken, Interlaken to Murren, Murren to Lausanne, Lausanne to Lyon, and then Lyon back to Paris. Can anyone venture an opinion as to our best option, buying each leg separately or purchasing a pass (Eurail, Swiss)? We can't price the individual legs yet as it's too early. Also, is it worth the price difference between 1st and 2nd class if we go the Eurail route?
Best option is to buy the Paris to Switzerland and Lyon to Paris in advance, nonrefundable. I am assuming you will spend at least the first night in Paris before heading to Switzerland. Otherwise you would really need to buy a full fare ticket to Switzerland because your flight arrival and journey through customs and immigration is unpredictable and you could risk forfeiting a nonrefundable ticket.
A Swiss Travel Pass or Half fare card may be helpful for Swiss trains. The price of these don't change, so you can add these up yourself at the SBB website. Just remember to click through on the "fare" button since the initial price shown on the first page assumes you already have a Half Fare Card.
Don't mess with a Eurail pass. Too many caveats.
And 1st class is totally unnecessary.
We did this last September (also because of great airfare sale): Paris for a few days, Lyrica train Paris to Lausanne (bought round-trip online in advance), bought Half Fare Cards in Lausanne and used them to buy Lausanne to Interlaken to Lauterbrennen to Murren tickets (one purchase), took Schilthornbahn using HFC, walked on trails around Murren and down to Gimmelwald, back up to Murren on the lift, spent our last day in Lauterbrennen (using HFC for tickets and bus) when Murren was clouded in, bought tickets back to Lausanne and picked up the Paris train. For these Swiss trips, the HFC was a break-even proposition versus buying point-to-point; if we had wanted to add Jungfrau, it would have been a big money-saver.
Didn't try to use Eurailpass because I was buying tickets only a month before travelling, and had heard horror stories about not being able to get seat reservations for pass use on French trains.
Second class was just fine.
I've done the Paris to Murren trip many times.
Perhaps there's a reason you want to go to Lyon? If not, you can take the 3 hour bullet train Paris to Geneva. (see www.seat61.com for info.) Once in Geneva you can get a ticket all the way to Murren. (Geneva to Bern, switch trains, Bern to Interlaken Ost, switch trains, and pick the cars that say "Lauterbrunnen" on the side. Then a cable car and short train to Murren.)
With that ticket, you can hop off at Lausanne which is in between Geneva and Bern.
I'd skip Eurail, but you might get a Berner Oberland Pass in Bern, which you can look up on the web.
Paris to Geneva can be as low as $40 if you get months in advance. Geneva to Murren is around $90.