No doubt Snape was the most qualified but Lupin had the biggest impact on his students. Lupin taught Harry the patronus and successfully taught the students about boggarts.

Unpopular opinion but Amycus Carrow shouldn't even be in the discussion since he taught Dark Arts and not Defence Against The Dark Arts. He also never taught Harry.

I agree. I would say that, ironically, Moody/Crouch Jr. was actually one of the better teachers (in the top three), because teaching the Unforgivable Curses and how to resist them, while illegal, had a lot of value, especially at the time.

Yeah, I'd put Moody/Crouch Jr. as the second best DADA teacher, after Lupin.

For me the top 3 was

1. Lupin

2. Moody (AKA Crouch Jr.)

3. Snape

Crouch Jr. was such a good teacher that he helped Harry resist Voldy.

He kinda stabbed himself in the back for that 💀

There's no competition here, the answer is obvious.