I'll make my take
My favourite anime character is Saitama (One Punch Man)
It may be kinda odd for some, because we know that when that guy arrives in front of monsters, he kills them instantly. Maybe to some, it kills the hype of a difficult fight, and I understand.
But to me, it doesn't. Even if I know Saitama's gonna blow the heck out of the big baddy, it always makes me hop on my chair out of excitement. (maybe thanks to building up the hype)
People may also think that it's because he's the comedic center of the anime. And even if it's absolutely true, there's something else.
To me Saitama is unique by the fact that he's the most "human" character I have ever known.
It's just his average-person look and behaviour that make him so great.
He's not a character with great ambitions like Luffy or Naruto. He never had a tragic event duri ghis childhood like a lot of characters have.
He's just human. He has flawed behaviours like greed or impatience.
Sometimes I get kinda sick of OP characters like Goku. He became kinda bland to me, let me explain.
Goku is a character who became extremely powerful to the level even some generic characters he fought back when he was a child are just mere germs to him now. And, contrary to Saitama, I see him more like a mindless killing machine than Saitama is. (which can be paradoxical)
The only issues Goku has are not being powerful enough against a foe.
Whereas Saitama has more common issues : Boredom (because of how powerful he is), loneliness (no one understands what being too powerful means) and lack of emotions (no excitement).
And I think that's why Saitama is my favourite anime character. Despite of his superhuman strength, we find a human who has the same issues as a lot of us. That's just something that I have a hard time to find in a lot of other protagonists