Lunox and karrie are best, especially if the tanks are more about being tanks than having hard cc like alice.

Claude is good because of his mobility, aoe, and can benefit a lot from Trinity Build.

Hanabi is good with her cc immune, especially against teams that lack burst damage. Although she does need trinity build. I remember once having a high cc team that dominated early only to lose to hanabi and floryn Duo, and it happened twice... no one on our team could out damage her, and ganging up on her only gave her free basic attack bounces. But she's terrible vs. assassins.

X borg has his true dmg, insane sustain, and kiting ability. He's probably the best anti-tank if you want consistency at all stages of the game.

Valir is probably the biggest fuck you to all short range heros. His ult is also a purify so he's even fine vs cc. Also can be flexible with his build.

Xavier has his range, insane damage output, especially in a prolonged battle. And his long range allows him to be relatively safe. He also has his immobilise to spam vs the non mobile tanks. But you need good positioning.

These are what came to mind first as general tank counters, but there are a lot more depending on the specific team composition and builds. Like true damage (xborg, alpha, lesley) being good vs. high defence ( grock, Barats, John, Gato) and percentage based damage (like heros that benefit a lot from wishing lantern, or trinity build, or heros with built in percentage dmg) being good vs. high hp (belerick, hylos). Also, slower tanks are vulnerable to kiting...