I've only had it for a week, so maybe I'm not of much help, but I've used it everyday and planning to keep using it as an everyday bag.
There is a huge difference in what fits in the mini and then the teen + small. I have the mini where only a phone, cardholder and keys fit, the teen and small are not clutches like that.
It is really worth it trying both the teen and small out in a store to compare them - I was sure I wanted the teen version, but ended up with the small instead after trying them out. First of all because size small looks better on my frame than the teen one, but I am also semi-tall, you should go for the one that suits your frame. Second of all the small version has a pocket with a zipper, that sealed the deal for me as I find that a necessity.
Regarding winter coats, depending on how big your winter coat is, my small fits with my puffercoat, but it doesn't look very stylish and is not as comfortable as when I wear it with my less chunky wool coat.