Hello! I am looking for hiking and activity recommendations for a 4 day trip for me, my husband, and 3 teen boys (21,19,17). We have booked 2 AirBnB locations (one in Brienz, one in Airolo) and are not sure which location would be best for outdoor hiking, mountain biking, etc.

Any suggestions?

Thanks much,
Christine

Both have an exdended (endless) hikiing trail network.
Brienz is the gateway for hikes in one of the best parts of Bernese Oberland (less crowded than the Jungfrau area) and up to the Titlis area.
The 2 most famous trails from Airolo go to Cruina - Nufenen Pass or italy and to Lake Ritom - Osco - Sobrio.
There are many spectacular funiculars and lifts as well as bus lines.
Brienz area:
Brienzer Rothorm (cog wheel steam train), Mountain Tower (gondola), Lake Gelmersee (rope railway), Engstlenseee - Jochpass /Titlis (bus and gondola), Grimsel Pass (bus), Susten Pass (bus), Aar gorge (railway).........
Airolo area:
Lake Riitom (rope railway), Pescium (gondola), Lake Tremorgio (gondola), Nufenen Pass (bus), Gotthard Pass (bus), Cari (bus), Bedretto Valley (bus).........

WOW! Great suggestions - thank you! If you could only pick one area as the base which would you recommend? It appears our Airolo AirBnB requires a 4x4 car to access and we were hoping to avoid renting a car given the threads we have read say there is plenty of public options. Is this true?

Wengen is very touristy. Airolo isn't touristy at all, despite 1 rope railway, 2 gondolas and 4 post bus lines.
There are some b&bs at Airolo, all at walking distance from the village center. I never heard of 1 with difficult access (accept Baita Cucurei, which is at a completely isolated place above Nante (not properly close to Airolo), at the "wrong" side of the Leventina Valley (more shade, less sunshine) and far away from any restaurant or shop.

Thanks so much - that is the exact place on AirBnB - good to know it is far from Airolo. We will go with Brienz. One quick question on transportation - the RegionalPass seems a bit pricey but with many benefits - would you recommend this vs getting a rental car for exploring the areas?
Thanks much!

A rental car isn't a good idea for the Jungfrau area, as most of the attractions can be reached by mountain railways, rope railways and gondolas only.
The following places cannot be reached by private car:
Muerren, Wengen, Junfraujoch, Maennlichen, Grosse Scheidegg, First, Brienzer Rothorn, Niederhorn, Schilthorn, Niesen, Schynige Platte, Harder, Alpen Tower (Planplatten), Lake Gelmersee, Trift, Jochpass-Truebsee-Titlis........, for others, public transport is just the more scenic solution: boat and historic rope railway to Giessbach hotel, boat to Beatus Caves, Postbus to Grimsel Pass.....
If you plan to explore the whole Bernese Oberland area, the Regional Pass Bernese Oberland might be the best solution. It's valid from Lucerne and Berne through the whole Bernese Oberland up to Loetschental, Brig and Montreux (Lake Geneva).
Some ideas about Swiss mountain railway fares:
Brienz - Rothorn RT: 94 CHF (47 CHF with Swiss half Fare Card)
Interlaken - Harder RT: 40 CHF
Wengen - Maennlichen RT: 52 CHF
Grindelwald - First RT: 64 CHF

thanks so much! I have a lot to learn about the area and how to get around most efficiently!!