Interesting. I give a lot of credit to Anti-Monitor and Galactus for really embodying the "Event Hero" name and adding a fun, scenario-like way to play Heroscape - which I know was a team effort but Bats gets the marquee at the end of the day.
That being said, I think I'll give my vote for
Green Lantern (Hal Jordan). Not my favorite Lantern design, but it's elegant and brilliant and a lot of fun.