The Dakine Heli, Heli Pro, and Heli Pro DLX are all decent choices if you want to go the Dakine route. Personally I would go for the Heli Pro DLX since it has more back padding, horizontal board carry, and waist strap pocket. I have the Heli Pro and find it a little uncomfortable carrying a board vertically with the little amount of padding.
I've tried on the Burton AK 15L before and it's pretty damn small. The contoured back padding is super comfy too, but I think the pack is pretty expensive for a 15L.