Greatest comeback in odi is easily afg vs Australia. Literally this has never been done before lol, you only see this type of stuff in hollywood movies.
In t20 cricket the greatest comeback has to be Aus vs Pak 2010 and 2021. Both situations were next to impossible for Australia which was 48 of 18 lol. But I'd say 2010 is better. Mattew wade got lucky by some rubbish bowling and some rubbish fielding especially hasan Ali while hussey was dominating top tier bowling.
When a batter is in such form, theirs honestly nothing you can do.
West indies vs England also comes to mind, like who could have predicted a tail enders chasing down 22 of 4 and winning the world cup for his country? What a game.
In test idk, Theirs alot of great test comebacks from impossible positions. Lars's one wicket win, Wi beating aus by 3 wickets chasing down 418, Steve Smith's iconic 211 knock.
I'd say the best test would be England vs aus Leeds 2019 where eng won by 1 wicket despite being bundled out for an embarrassing 1st innings score yet and being forced to chase 370 something in the 2nd innings