I think it's the maxi..it measures 22 inches...it's on BF right now.
That is the one I just returned, because I either ordered it wrong, or BF filled it wrong. I had intended to order the smaller one. The maxi was a little too big for me, but a great bag nonetheless...someone please give it a good home!
There is also this buy it now on eBay; not sure if this is a size people are looking for:
I believe that is the Medium at 15"
The Maxi is pretty close to 22" wide.
The maxi is the one that I have (22 inches) and I quite love it. But it's definitely a lot of bag!