mine would forever be "calvin and hobbes". the art is superb and the writing is soo funny that it's not just for kids. it turn philosophy and science into a work of art.
the greatest ever comic character born is no other then TINTIN, if you dont know you have missed something. get tintin comics books and enjoy each and every dialogs and pictures.
The coolest comic I ever read was "Astro City". The stories are told from the citizens point of view and not the superhero. Add to that the inside artwork was great and cover art by Alex Ross, you have a winning combination.