I think most people would think of Justin as Jimmy. While Michael was first, he was only there 1 season. Justin was there the last 3 seasons, so that's the one that sticks.

"You need me. You wouldn't be much of a hero without a villain. And you do love being the hero, don't you. The cheering children, the swooning women, you love it so much, it's made you my most reliable accomplice." -- Lex Luthor to Superman, Question Authority, Justice League Unlimited