I was debating between the medium and large. For awhile, I really wanted the large when I saw it in person. I didn't have the opportunity to purchase in person ultimately (a friend picked it up) and I was relegated to looking at the sizing on ebay and shopbop. The large is really large. The medium is a great size for an every day bag and it will fit a ton of stuff in it. I mean, really..a ton. Last week I took it on the plane with me and had my LV zippy wallet, LV cles, ipod touch, cell phone, large longchamp pouch, bottle of water, magazine and a bag with a muffin in it. It zipped easily. I think the large would be good if you just needed to carry even more - but the medium is fine for me for every day.