I would really recommend staying at Franziska's place. Franziska is a really nice person to discuss with but also helpfull when you need (and a super good cook!). The flat location is central, in a lively but quiet neighborhood. Regarding the flat itself, it is clean, sunny, nicely decorated, the kitchen is more than fully equipped and the bedroom is comfortable. Indeed the livingroom is not for sharing when Franziska is here, but the flat was big enough so that I did not feel the need of it. I would definitely go back there if I have to stay once again in Zurich!