The anonymity set is the best theoretically possible - everyone in the shielded set. It's the same for zk.money and tornado - the difference compared to tornado is that tornado has fixed amounts.

There's no possible attack to deanonymize the full zero-knowledge model beyond the utilization of always existing metadata - which needs separate solutions for every such system. In practice, zcash doesn't have that many users, so the anonymity set isn't big, but that's a separate issue to technology.

The question which one is better in practice right now is a more complex one. Even a perfect solution like zcash/zk.money is useless if (just a random number) only 3 people use it, and ringct with (again a random number) 100k separate people with roughly equal tx count would obviously win. My estimate is that tornado.cash is the most anonymous. Monero is hard to estimate because there's no way to know how many spent outputs are known to the American government and/or cooperating chain analysis companies. Is it <1%? Then it's probably second best. Is it 90%? Run away.

Last but not least monero can be deanonymized retroactively by quantum computers. Tornado, zk.money and zcash can't - they can be robbed (monero can be robbed too, obviously) but that's a much better failure mode.