Brienz: Information from Dick --
I like to stay in Brienz, 20 minutes by rail or road from Interlaken. It is a woodcarving village on the Lake of Brienz in a pretty setting. If the weather is good go up to Grindelwald or Murren for the day. If its not so good you can easily go to Bern or Luzern. I like the Weisses Kreuz hotel across the street from the station.
Jura Bernois Tourisme Watch Valley
Lauterbrunnen: Information from Goose --
Get up into the mountains. Lauterbrunnen is a good base from which to explore the Jungfrau region. It is high enough into the mountains and has a major rail station from where you can set off to the smaller and quainter villages. The rail track from Interlaken takes you up and past Lauterbrunnen anyway. But staying in Lauterbrunnen will give you more of an Alpine experience.
SBB Online - Swiss Federal Railways
Switzerland Tourism Switzerland. get natural.
Wengen: Information from Roger --
Wengen is one of my favourite places. Beautiful, no cars, stunning scenery and some nice hotels. Good for walking in the summer too. My favourite hotel there is the old-fashioned family style Falken, though it can be rather like Fawlty Towers. There probably will still be snow in the village in late March, though much should have melted. You would need good high waterproof boots for any walking outside the village. You can also take trips on the mountain railway to Grundelwald etc. Also to Eigerglacier but very expensive. The valley towns such as Interlaken are OK but not so atmospheric. And not so sunny as they are more shaded. But of course better places for excursions.
Wengen: I agree, Wengen is a great little village to make your base and high in the Alps. If you stay in Interlaken you are really out of it. I've stayed at the Hotel Bellevue. The owners Judith and Andreas treated me extremely well. Very nice people. Great buffet breakfast included in price. www.bellevue-wengen.ch/e/