Feb 11, 2016 - 9:03 AM
I wouldn't worry too much about temperatures when it comes to choosing a town. Even if you stay in Interlaken you'll go into the mountains for your day trips, so you need to deal with possibly lower temperatures anyway. You don't need winter clothing for regular day trips. Multiple thinner layers work just fine, and allow you to adapt to different temperatures throughout the day (see here).
There are other factors to consider: if you value a lively town and a good choice of restaurants/shops, Interlaken is the better option. If you want to explore more of the Bernese Oberland, not just the Jungfrau Region, Interlaken is more comfortable because of better train connections. Wengen is the place with much better views, and where you can start hiking right from the hotel.
There is a third option: Lauterbrunnen is down in the valley so a bit warmer. It's surrounded by nature, and offers easy access to both Wengen and Mürren. It is tiny though.
Once you have made a choice, feel free to ask for help in the accommodation forum if you need hotel suggestions. Hotels in Interlaken can be found on the page I gave you before.
Last modified on Feb 11, 2016 - 9:04 AM by Arno