Ticino (where I live) is beautiful and really is not to be missed. It is completely different from the rest of Switzerland and would allow you to experience the third culture of Switzerland (the Switalians as I playfully refer to them). The lakes are beautiful and it is much warmer than the rest of Switzerland. There are mountains that you can go hiking in and boats to take out on the lake (Lago di Lugano or Maggiore).

As for Interlaken if you want and extremely small town packed with nothing but tourists, go right ahead. Yes Interlaken has river rafting and paragliding, but the Swiss don't really go there. I had a good time when I went river rafting for the day and visiting Hooters Interlken was slightly amussing, I wouldn't go back or want to spend much time there.