[HoMM3 on-line Tournaments] "Favorites to Battle"

And another interesting observation – three Necropolises, three Ramparts, three Dungeons, and three Fortresses made it to the semi-finals. You could write a research paper about the strength of these castles.

I'll add that, according to preliminary results from the current season, these four castles are the leaders after the Conflux. But since no one plays as the Conflux, it turns out that these four castles are leaders by definition :).
After the current season ends, I will post a table with all the data for each castle.