Out of my own characters, it would probably be Henry Rider just because of how realistically fledged out she is. She's bright and cheerful, always cracking jokes, but can be serious when she needs to be. She's fiercely loyal to her friends and family, but can still feel jealous, or bitter, or betrayed, and lash out at the people she cares about just like a real person. In some scenarios she's dumb as a rock, but in others she's a tactical genius. She can be loving, cold, caring, cruel, confident, and vulnerable, and it all feels natural instead of contradictory. Sometimes I find it hard to believe that a hack like me managed to write a character like her.
And have I mentioned how incredibly humble I am?
When it comes to other people's characters, I'd probably give it to Vin from Mistborn. With characters like Rey, Captain Marvel, and Alloy being pushed as "strong female heroes", I always point at Vin and yell "Look! Its not that freaking hard!" She's strong, independent, has her own opinions and goals, and can kick twelve different kinds of butt before breakfast. But she's also a vulnerable, flawed, human-sized knot of insecurities. And while she ends the trilogy as the most powerful allomancer who ever lived, able to take on entire armies by herself, she doesn't start off that way. She grows throughout the story, going from helpless street urchin to unstoppable tornado of death in a way that feels natural. And even at her strongest, she's not invulnerable, and constantly has to battle her sense of inferiority and fear of abandonment. She was actually a huge inspiration for Henry, and she has one of the best written character arcs I've ever read.