I've got the 12". It's all the store had when I bought mine. I don't think it rotates nicely so I don't rotate it at all anymore. It is the one that is next to my machine for paper piecing when I just need a quick slice.
Having said that... It isn't wearing as nicely as my big Fiskars mat. It doesn't appear to be very self healing and is looking really funky. It doesn't get a lot of use but it still looks terrible considering its age. I wish they could have used a better material in making it...