When I first started reading JLA during the Satellite Era, Oliver Queen stood out right away. The JLA was a bunch of mature, father figure guys that were pretty much always right.
Green Arrow on the other hand, was irrational, a loudmouth that alienated people. He presented a definite point of view, and he was not always objective and sometimes (most of the time!) was "wrong."
I guess i like Ollie for the same reason Dr. McCoy was my favorite character on the original Star Trek.
Also, I liked that he had connections and relationships with the other heroes. He was buddies with Hal Jordan, romancing Dinah Lance, and best friends/rivals with Hawkman. It was Avengers-style approach to a team, where all the characters hang out with each other and have real relationships as opposed to showing up when there was a crisis.
When I started reading JLA by Brad Meltzer after a long time, I was a little disappointed Ollie wasn't going to be back, but he more than satisfied me with his characterization of Red Arrow. I liked little wonderful character bits, like the idea that he keeps a picture of his daughter inside his quiver. That's one thing I like about Meltzer: he made missteps, but the characters were emotionally three dimensional.