I own Union Atlas & Burton Cartel Re:flex and I have to say, so far I favor the Cartels even tho they are too big so I cant get my boots centered proporly... They are just so comfy and autocant is something I like really much!
I got the cartels in size L with 10-11 sized boots, and its too big for my boots to get centered. Id recommend going size M with them. But, its better if you can take your boots to the dealer and check yourself to be 100% sure.