I got an STM bag from a macshop here, and love it.
*goes off to find link*
http://www.stmbags.com.au/smallloft
This is the one that I got. My macbook fits very snugly into it, no troubles.
I suggest calling or visiting a mac shop, rather than 'some store' where they're more likely to know their stuff, AND are likely to have both the bag and the same model laptop in the store. If they can't give you a demo, take in your laptop and try for yourself.
As for the bags, I was pretty impressed by them. It was either that or a Crumpler for me. If I'm gonna be carrying a laptop around, I want to do so in a quality bag, but I also wanted one that didn't look like your average plain black bag, which would be an open invitation for a slashing
I suggest you just go down to your nearest mac store and check them out for yourself.