best turkey burger?
Best? That's a difficult one given the turkey (many places just serve a chix-breast) and they only cook it "done."
That said, I'd try Barney's Gourmet Burger, various East Bay location, Shattuck Ave, Piedmont, College Ave, Solano Ave. I had one years ago and it was about the bun, lettuce/tomato and condiments. People have told me recently it's pretty good. Thing is, I only get burgers about 4x a year so I just get beef.