I have all 3 sizes of the boy bag & actually love them all- but for different purposes.
The medium is my favorite as a daily bag. It fits a good amount & I love the crossbody option when I need to be hands free. It’s great for day to night.
The small is my favorite. I wear it mostly crossbody & it’s adorable. But it’s the least practical. I really have to pare down my essentials. It’s a great going out bag & I love it. But there is a bit of Tetris to take out my phone. I can use it for a daily bag- but not really long-term. (Ex. On a trip I would bring this & a tote).
So it depends on your needs/expectations.
Try putting your stuff in both sizes & then you will know. I saw a lot of utube videos but trying my own stuff was more helpful.
Good luck!