I would be the practically unkillable Wolverine, no doubt about it. Because of his healing factor he is very old -- how old, no one knows. This has allowed him to live a very interesting life. Anyway, I think he has one of the most fascinating nemesis relationships with his equally tough adversary, Mystique.
As a superhero should be the opposite of what you are I would have to be the FLASH. Its the only way I would do things fast. In real life I m laid back, like to take my time to smell the roses. As the Flash I would have to be quick.