We stayed 5 nights in Wengen, and I would recommend it over either Interlaken or Grindelwald. We combined the following sites:
Jungfraujoch (first train), took Eiger Express down to Grindelwald terminal then train to Grindelwald. Took cable car up to First for thrill walk & mountain carts. Then took the train back to Lauterbrunnen and on to Wengen.
Combined Murren (and Allmendhubel and Gimmelwald) and Lauterbrunnen
Visited Lake Brienz for half day: took the train from Wengen to Brienz, then the boat to the Geissbach funicular. Lunch at the hotel terrace, then boat back to Interlaken and train to Lauterbrunnen for dinner.
Interlaken is not a charming town. It is a transportation hub. Grindelwald is a bustling resort town with lots of traffic and tour buses.