About Lugano, Locarno, and Anscona, which one to stay in depends on your tastes. We spent all of September 2001 in Locarno. As others have said, Locarno is better located for travel to Stresa. It's right next door to Anscona and a short train trip away from Lugano. All three have something to offer but I'd choose Locarno. You could even stay in an apartment as we did (details at website).
See photos and travelogues of our month by the lake in Locarno including Lugano, Anscona and other Swiss side trips: http://www.ualberta.ca/~pletendr/swiss/