im actually in a pretty convenient position to answer this question, as i purchased the sf waterfield designs sleeve for my girlfriend's 15" mbp, and the tom binh for myself...
the sf bags sleeve is just that-- a sleeve. if dropped, it would offer about 1/4 of the protection that the binh sleeve would. that being said, this sleeve is thin, and can easily be slid in and out of backpacks and bags, etc... the interior of the sleeve is as smooth as a baby's behind, and with the vertical velcro flap, dirt or anything would never get in. (i would def. choose the vertical opening over the horizontal).
the tom binh bag has a couple advantages in my opinion. it is about twice as thick as the waterfield sleeve, but that is because of padding and a harder 'shell' than the waterfield case provides. (i wouldnt be as wary dropping it, or packing it in luggage in the binh bag). furthermore, the brain cell has rings on either side near the zipper for attaching a shoulder strap. this way, the sleeve-case can be used by itself over your shoulder, or slid into a knapsack or whatever... a big bonus.
the customer service from both suppliers was incredible. as is the crafstmanship, ship times, etc...
either way you can't lose.