The Washington Post ran an article on the history of the DC/Marvel rivalry in yesterday's editions. It's good stuff.
I was a DC-only reader until about 1984, when John Romita Jr.'s art and (hard though it is to believe) Chris Claremont's storytelling on Uncanny X-Men rocked my teenaged world. Later I shared fast-food fry-cook duties for a summer with a Marvel Zombie who loved nothing more than discussing the minutiae of Marvel's "What If?" title. ("And then Crom buried Mjolnir under a mountain, because it was too powerful a weapon to exist on his world!") He wound up completing my indoctrination.
My only complaint with the article is that the Post went to Big Planet Comics as the authority on such matters. In 1989, when it was still on the 2nd floor of a dump in Bethesda, I was a regular customer of Big Planet Comics. At the time, the cash register was well back in the store, not at the front. One Wednesday, after I had paid for my weekly stash, I paused near the stairs to look at the covers of some comics I hadn't noticed previously. And the owner yelled at me: "Don't keep browsing after you've checked out! I don't want you walking around the store with a bag." In other words he accused me - a fairly loyal and regular customer - of being a thief.
I looked at him like he was crazy. Then I smiled and said, "Well, the good news is you'll never see me walking around your store again."