The ranking for players is based on stats. For each class/spec, I came up with a short list of the most important stats. The players get ranked by this weighted average, and their percentile in the list is their score.

Guilds get ranked by the power score of their best 25 players.

Did you see any of the Top Items? I think that's pretty useful, but may be hard to understand, I'm not sure (its always easy to understand when you wrote it).