Here is an article from straight razor magazine that gives lots of info on SRD strops:
Straight Razor Magazine: Review: Straight Razor Designs - The full strop line
I'm not all that familiar with their razor/strop sets, but I'm sure that you can get them with a variety of strops. As Hirlau suggests, price can come into play, especially since most of us have managed to nick or cut our first strop while learning the technique (you'll also notice that their strops are made in such a way that you can buy replacement components instead of a whole new strop if this happens). That doesn't necessarily mean that you have to start out with a sub-par strop, but it is something to consider when buying your first one. Of course, YMMV, but I don't think you can really go wrong with any of the SRD strops.