I am 5’7” and I. Have the 30 and in my opinion it’s perfect. It holds a lot of stuff but it still looks very elegant. My sister is a little shorter than I am, she has the 35 and she’s happy with it but if she were to do it again she might choose the 30.
Depends on what you need to carry. I have both the 35 and 30 and am 5'1. For university the 30 would have been too small, but for everyday I prefer the 30. It's just more compact and structured than the 35.
Im 5’7 as well, would recommend either the 30 or 25. My first speedy was a preloved DE classic 35.
After taking the 35 out to the mall and spending a whole day with it, I immediately listed it for sale that night. It’s an uncomfortable big bag. Don’t recommend it, especially if it doesn’t have a strap.
Highly recommend the size 25 bandouliere. That’s my most used bag for casual outings. For a work bag to fit the laptop, I wouldn’t recommend a speedy but a Neverfull.