Who was best not WC best player?

i have no clue because it matters the time control and what color there playing as.

If not the best and not candidates but I really like them:
Ulf Andersson (endgames)
Jan Timman (positional play & strong opening knowledge as well)

Level of play : Ivanchuk. His best games are the highest quality of chess played by humans or close to it.
Contribution to chess : Korchnoi. I think he's superior to Euwe and maybe Spassky in that respect, comparable to Petrosian and Smyslov.
Class : Keres. His best chess was extremely elegant and precise.

yes i too think there is a strong case for Ivanchuk
but he was inconsistent
he was capeable of www.chessgames.com/perl/chessgame?gid=1060207
but also of www.chessgames.com/perl/chessgame?gid=1485885

Well, Bronstein was a half point away from becoming world champion, so he certainly was good enough. He gave in to political pressure, and threw the match, for many good reasons. Then he lived a life of regret, which is sad, because he probably made the right decision. Chess trophies and titles are not everything. Getting your father out of the gulag ranks higher.