This is strictly from memory but I believe it was a team of 6 Chansey that won the first ever world tournament in 1998 in Japan. Each Chansey was basically a different type special users with a Counter Chansey on the physicals. After this tournament the 1 species rule was implemented. As well as the Evasion ban... I could be off on this though. A couple of points to add to this discussion: 1. The answers you will get will be by and large opinion as this is an opinion question. It's already been pointed out that the Pokemon that are vying for top spot play different roles in the metagame. Whichever role the poster values will by and large be ranked higher in that players mind. So whether or not someone thinks its Egg or Tauros probably comes down to whether or not that player values sweeping more than supporting. 2. From what I can tell this discussion is focused on "pure RBY" and is not considering tradebacks?