I've got a Proporta case that was sold to me when I got my TF from Currys. It's not great. I mean, it does the job, but I find I have to coax the chunky zip around the edges of the tablet. This means the top corners are quite harsh / hard where the corners of the tablet force themselves into the zip and I'm also mildly concerned about what ongoing zipping / unzipping is doing to the condition of my Transformer.
Zippers and a tight fit do not play well together. That's why I stick to cases with flaps.
If you're going the Kensington route (because they are nicely made), the next size down from the one mentioned above is this one for $5 from Amazon with free shipping (2-day prime for me). I'm picking it up just because I liked the one that was too large. Solid quality case.