Dick Grayson as Nightwing or Robin. Like a razor's edge separates him from Tim Drake as Robin. Two of the best reworkings of an existing hero ever seen.
Favorite group - Legion of superheroes - I loved the original run, especially Levitz. But I liked the reboot, and I thought the 3-boot had some promise.
Favorite Superhero - Karate kid from the legion.
Favorite Mainstream DC Hero - Nightwing.
Favorite Marvel - Captain America.
They are all "normal" just super highly trained with equipment, and they are all straight up good guy. Cap being a perfect example of an example of what a hero is (I love Superman for the same reason, but his power set can make him boring to read in the hands of an average writer).
Thinking about this, and reading some of the answers, it reallly shows how much so many comic characters have changed, backward and forward and in all directions over the years. To name my favorite superhero(s), I feel the need to qualify, to narrow down the era I know them from.
Sort of like saying Dungeons & Dragons is my favorite RPG.
My favorite varies, often with the writing. If I think the character is being well-written and the stuff going on for them resonates with me, they may be my favorite. If that shifts, someone else will become my favorite.
Some who keep coming up into my notice as favorites:
Wonder Man
Element Lad
Lightning Lass
Captain Marvel (Mar Vell)
Ms. Marvel
Banshee
Cyclops
Havok
Wolverine
Beast
the Human Torch
Vortex (from the Elementals)
Green Arrow
Goliath (Hawkeye version)