As for the rest of the 10-7 group.
Spawn is the essence of the 90's in all ways both good and bad. He's the most successful comic of all time from outside of the Big Two. He's had everything one could hope for. He's well known to the mainstream. He's had some spectacularly great stories and some horrible ones. Lots of the people who voted on this list, whether they want to admit it or not, have followed this character at some point or another. In many ways he's the greatest achievement in indy comics, and also one of the worst. The amazing success of this book, which would sell to the #1 spot at times, inspired dozens of terrible imitators, made people think they could over expand (which led to many companies closing), fueled the speculator market, and also kicked ass and led the charge of movies and shows based on indy books. This is a really long way of saying, he fully belonged in the top 10 and that without him, our surprising #1 may not have ever reached the levels he's reached over the last few years.
And just ahead of him is a guy that very very nearly made my list. Jesse Custer is the star of the best book ever to feature Satan being shot in the face, Hell freezing over, God as a villain, a vampire asshole, and a guy with a dick carved in his bald head. It's also probably the only book with all those things. Great book, Jesse is a great character, but in the end I went with Cass who should have been much higher. Bubba, I will say you should only buy the first two trades to start with. As chap said, this is a very love or hate book. I loved it, but you may not despite similar tastes.
Then there's Kyle. Hal is not better than Kyle, but Kyle also isn't better than Hal. Stop it. They are both great characters. To me, Hal is the main GL. However, I never got the folks that hate Kyle or the ones that hate Hal. Both have had some great stories, both have had some awful stories, both are only as good as the writer. Just like John and Guy. Erase the Hate.
I am really pumped for Blackest Night.