Rigid3D yes, he's definitely up there with Nyl in terms of quality, Big Johnson, not so much but decent content, I don't think I've seen anything game changing from Janner in some time, and Amazonium is also pretty good, although I find that some of their content is somewhat "copycat" in nature, I don't mean that in a bad way, I just know that once Nyl or Rigid does something, Amazonium follows up with something very similar to fill the gap.
Amazonium kinda works with them most of his/her time he is an assumed fan of their models and is always mentioned as some of the people responsible to pass them around their community,as for Rigid,the guy simply does what he wants,sometimes he does just cg,other times he animates,but with him you never know,just that the animations are always good(even if a little too loopy).Nyl we already discuss here,so i dont think its needed to get into a bigger depth on this comment.
Janner is kinda busy with his personal projects about the world of his O.C.s and some real life complications,so he was really stalled until some time ago.
Big Johnson is a relic from the times of the promissing nsfw artists of tumblr,guy refuses to give up,i give him that,and his style improved but his workflow is easily stalled by his real life problems(probably work) and the fact he was one of the first artists who made his animations very detailed in the motion part always ensured that he as guy who took a little extra time to deliver.
I'm actually waiting for Depraval deliver his Jill Valentine project,but the guy is learning still and seemed to be using some low end hardware and that cost him not only a lot of time to learn to deal with,but a lot of work and effort with mistakes and losses on his progress...
P.S:When i said Amazoniun is an assumed fan i mistook by the pronouce of the word on my mother language,i was meaning that he is a declared fan of their work(Rigid and Nyl)