I'm around 5'3 and approx 110lbs, and I think he 30 looks best. I have the multicolor white speedy 30 and a speedy b de in 30. I've had the 35 and 40 classic speedys before, and I felt it was too luggage-like on me. Definitely can't do cross body for me with anything larger than 30.
I have the 35 , and I brought mine a month ago like you I didn't know whether I wanted 30 or 35 , there's a lot of YouTube videos and the threads here are useful. I'm about 5ft here's me with my 35
In the end I want for the 35 as I wanted the extra room if I needed it , good luck !
I had a 30 sold it. Bought the 35 in mono instead. I like the opening better on the 35. I am only 5'1 and prefer the 35. But as far as wearing the speedy b , i like the 30 better because 35 crossbody on me is just to large looking. Hope this makes sense