I would go with the 12" as gliders like to jump in the wheel, and they need lots of room to do their tricks.
Have you considered getting a Stealth Wheel from sugaraesattic? , these are made specially for gliders and in my opinion are the saftest out there, as they do not have a cross bar. <img src="/ubbthreads/images/graemlins/thumb.gif" alt="" />
Stealth is the best and you can't buy Wodent wheels at a pet store. You are probably seeing the Silent Spinners, they can be dangerous for Sugar Gliders.
Keeper of Handprints on my Heart, You left your Footprints on my soul. My precious loves that left to quickly, Peanut, Katie Isabella, Kiwi, Bonnie and Monroe.
Spread your wings and glide free of pain, Until the day I see you again.
i have that same one for my little ezmyrelda. she loves hers. eventually i'm going to buy one of those that have sandpaper so i don't have to trim her nails. but i think you will be happy with that wheel...