When Graciemag got votes from multiple high level/world champion/old school guys who were the best BJJers of each decade, Rickson won the 80s and I think it was unanimous and they pretty much all said he was the best ever. He definitely won, I could be wrong on the rest but can't find the article.
Paulo Fihlo said that he was way better than anyone else he had ever trained with. That is a guy who is making comparisons to awesome BJJers.
Andre Galvao said Rickson smashed him when they did positional sparring from mount. Galvao could never escape and always tapped, Rickson always escaped.