Bearing in mind efficacy and my vape preferences, the winner between cotton (organic and Japanese) and rayon is rayon for me. I'm still dialing it in, but my best rayon wickjob is simply amazing with how well it wicks. KGD isn't that far behind, but there's that whole cotton taste thing going on. I prefer the flavor delivery of rayon. The whole flavor and nothing but the flavor. Unless you over stuff it, then it's a bit nutty. But, that's user error.
KGD will wick like a dog with its tail on fire, but when vaping the same juice out of the same builds and the only difference is wick material, I go with rayon's flavor.
LIfe's too short and wick is too cheap to not have a go for yourself. If you don't want to commit to a box of rayon, I'm sure that one of us would be more than happy to stuff some in a baggy and stuff it in an envelope headed your way.
EDITED TO ADD: Woah, we got a wick forum?!? /happydance Thanks admins.