There are 9 leaderboard displays in the lobby. The categories are: most gold, highest levels, highest wave (Casual competitive only), highest elo, top supporters, most rubies, most time played, most gems, and highest infinity castle floor. The 100 highest players will be on their respective category.
To get onto the wave leaderboard, the map needs to be the weekly featured map in Classic Competitive. There are categories in this leaderboard for all difficulties, and each one individually. Leaderboards will update when you rejoin lobby.
The Elo leaderboard is capped at 100,000 elo. The highest wave on Classic competitive leaderboard is capped at 250 waves.