Wow.. you're right. There's a huge variety of thicknesses and sponge hardnesses available on all of the 61 Second rubbers. This wasn't always true - two years ago they had Kangaroo and Eagle on sale, I bought 2-3 sheets. NO thickness option, and only two sponge hardnesses (med. soft, med. hard IIRC).
As for which one to buy - I'd go with the thickest sponge UNLESS you're using a balsa blade, or are a pips-out blocker/hitter (which wouldn't apply here...
). Hardness? Take your choice. I'd personally buy two sheets, one of which would be the hardest and one the softest, and then try them out back-to-back on the same blade, but that's just me. You might end up playing with the hard one on the forehand and the soft one on the backhand, or you might decide you might like the soft one on both sides (in which case you shell out another $10 and buy another sheet) or you might get totally confused and can't tell the difference between them (which I think is what will happen..
).
By the way... stay away from Ckylin. If you're curious as to why.. well, then, BUY a sheet of Ckylin and find out.
It's one of the very few rubbers that I can safely say feels WAY different to anything else I've ever tried, to the point that I couldn't use it at all. Just be prepared to wonder what they were thinking, what with all the "Chinese Blue Fire" nonsense.
Iskandar