I struggled with this pattern; it has a new stitch and the tutorial they provide was a bit obtuse.
The rhythm of the new stitch soon made itself clear after I work a bit and I am so glad I stuck to it!
This is the medium size and it has a lot of stretch since the ribbing continues up the whole hat.
It fits me just fine so I would call the middle size medium.
I used some left over DK weight yarn on # 6 needles.
I liked it so much, I am casting on another one!