I'll keep that in mind. Thanks :)

SWISS HALF FARE CARD
It depends on the fares you will get for your Paris - Switzerland and Spiez - Milan tickets.
If you plan to do a lot of local travel within the Bernese Oberland, the Home / Regionalpass Berner Oberland might be a better solution

I think this is what I'm looking forrrr. Thank youuu

Half-fare Card is hard to figure out sometimes as you do not know how much you will really be traveling - and with a pass you may travel more as you need not think "is this worth it to me"?

I must admit that I prefer to direct people to ways to find answers on their own (give a person an answer, and they have an answer; give them a way to FIND an answer, and they have a key to the future) – but that’s just me. If what one wants is current information about transportation in / through Switzerland, I’d look no further than what neckervd posts. JMO.

neckervd is a real helpful always knowledgeable person - a local. Great resource.

But why would not the Jungfraubahn Pass be better for someone only going to Jungfrau Region? I see no reference of Lucerne area. Buy either pass locally at any stations - no need to buy ahead- assuming you get discounted ticketsfor coming and going to Jungfrau.

The RT ticket to Jungfraujoch costs 99 CHF with the Bernese Oberland Pass and 69 CHF with the Jungfrau Travel Pass.
The Bernese Oberland Pass is valid from Interlaken up to Berne, Gstaad, Lenk, Adelboden, Brig, Lötschental, Kleine Scheidegg, Grimsel Pass, Susten Pass, Lucerne, Brienzer Rothorn (from both sides) as well as between Lucerne and Berne via Langnau.
and grants half fare for
Gstaad - Montreux. Gstaad Glacier3000, Brig - Oberwald - Andermatt, Grimsel Pass - Andermatt, Grimsel Pass - Oberwald - Nufenen Pass - Airolo - Gotthard Pass - Andermatt, Susten Pass - Andermatt, Lucerne - Titlis.

The Jungfrau Travel Pass is valid for
Interlaken - Lauterbrunnen or Grindelwald - Kleine Scheidegg - Eigergletscher
Lauterbrunnen - Muerren (via Gruetschalp only!)
Interlaken - Harder and Schynige Platte
Grindelwald - Bussalp/First/Grosse Scheidegg/Waldspitz
Grindelwald - Maennlichen or Kleine Scheidegg - Wengen
and nothing else

So, all depends on what the OP will do

So for a 2-34 day stay in Lauterbrunnen only and if taking Jungfraubahn train and other conveyances it would be Jungfraubahn Pass or Half-Fare Card or none if just hiking?

Thanks again neckervd for taking so much time to lay it all out.