Male and/or female.
Someone with a character arc that causes them to experience actual growth. Someone who struggles. Who's a real person and not just a series of character traits.
Of course, when we actually get characters like this, more often than not anime fans hate them and call them whiny bitches because otaku don't understand how real people work.
This is so true in the anime community. One example of this is Osamu from World Trigger. He is not the typical battle shonen hero, but I think he is great because his character adds more to the show. He has to use his head, and he fails often. I love when characters have to use means other than their own power (in battle) to achieve their goals; that is why he is so great in my opinion.
HEIL UMARU!
Someone just like us.
Secretly a nerd that stays behind a PC / console all day long.
And is just 'slightly' better than us plebian nerds.
I love characters that have a similiar look to me ( someone other that I know ), and normally represents themselfs nicely and in a peacefully way.
For example this girl is the same as my sister, same age, different at school and house ( yeah, I've seen kinky shit from her, as we went to the same school for 2 years, from normal to idkwhattosay at house )
In other words, someone who the outside world thinks is perfect but is actually a terrible person whose terribleness we're supposed to find endearing somehow?
Umaru is literally just a slightly less shitty Kirino, who is one of the shittiest characters I've ever encountered.
(yes i am aware of the irony of holding this belief while using an umaru avatar)
Someone who is passionate about something but doesn't let that passion control their lives. They still need to be able to control themselves. Someone who has the self awareness to not act arrogantly when their is nothing to be gained from it. Someone who strives to make intelligent moves.
I want someone who doesn't let arrogance and the like control their lives in every aspect, someone who is able to get along with people when it is beneficial.
Lelouch is pretty much an ideal character.
Not used for the butt of some dumb joke all the time or pointless out of character fan service. Relatable, interesting, goes through character growth negative or positive. Characters that are fleshed out and human.
Some of favorite protags are probably Utena from Revolutionary Girl Utena , Kenzo Tenma from Monster, Chiyuki from Death Parade, and Shion from Shion no Ou.