This is a tough one for me. Couple of reasons.
First one is that I have a hard time narrowing down my favorite character!
When I first started reading super hero comics it was Spider-Man. Then for a while it was Hawkeye. Obviously from my Avatar and Username I am quite fond of Moon Knight. And that's just Marvel!
Second is that most of the creators involved with these characters were actually highly rated.
I'm going to go with an underrated creator for a lot of my favorite characters - Steve Englehart.
He was the writer for Amazing Adventures when Hank McCoy turned into the blue (or gray) furry Beast, he brought Patsy Walker (former Romance heroine) into the Marvel Universe, had a long run on the Defenders and introduced Valkyrie to the MU, Avengers/Defenders War; Celestial Madonna; Serpent Crown.
He left Marvel for DC and did this:
He helped bring Batman back to the pulp oriented, gritty character that he started out as.
The Englehart and Rogers pairing was described in 2009 by comics writer and historian Robert Greenberger as "one of the greatest" creative teams to work on the Batman character.
When he returned to Marvel his stint on West Coast Avengers was pivotal in transforming Hawkeye from a brash insubordinate into a confident and capable leader.
But he is rarely mentioned when you talk about comic book greats. Should be.