I just got the 30 and I think its the perfect size. I also agree that the 35 looks alittle too much like luggage, unless you like the really saggy look (which can be really great too!). If you are looking for a more structured handbag look, the 30 is awesome.
I choose the 30 too (I have a 25 and a 3o). The one time I saw a woman in real life at the mall with a 35, it just looked a little silly to be honest. Way too much like luggage. The 30 holds a tremendous amount. I love mine.
I got a Speedy 35 because I hate the opening of the 25 and 30. For me it's too small, and I don't like it if I scratch my hands when I go in and out. Go for the 35 - it's very special and not so often to see..