The X-Men where pretty much my first real introduction into comic books. X-Men Vol 2 issue #13 - it was the second part of a regular X-Men story. It had to do with a childhood friend of Charles Xavier who had become an enemy. I of course was swept into the 90s X-Men cartoon. It pretty much informed me about everything I needed to know about the X-Men. I followed the cartoon and the Comic based on the series (it just retold the same stories, though) What continued to get me more involved with the X-Men was the "X-Ecutioner's Song", an X-Men cross over that I simply will never forget. I didn't know half the things I know now about the X-Men, and all the characters - but that single cross-over informed me so much about every team and a slew of mutants I hadn't even heard of. I've reread the story many times, and often learned or understood something new about the tale. This was an excellent time to be an X-Man fan, and a great introduction into the series, and comics in general.
Spider-Man was my second comic of choice. I began getting the series pretty much because of the Animated series. I knew nothing about Spider-man at that point, and I knew even less about everything that was happening in the comic books. So it might come as a surprise that I began reading Spider-Man during the Clone Saga. A story line that ripped Spider-man's world in half, but exploded with shocking developments and plot twists. I believe the first issue of Spider-man I read was when Peter was in prison, framed for a murder his clone Kaine committed. Ben Reily was simply too cool for words, and I absolutely adored the Scarlet Spider costume. These issues where a challenge to get into, and learning about Peter's history during this time was no easy task. The Animated series cleared up a lot for me, and I quite enjoyed the whole ride, as twisted and out of control it might have been. I also actually believed Spider-man was really going away, for good, in an issue of Spectacular Spider-man, where Bel Reily took over for Peter. It wouldn't be until years later that I'd get back into Spider-man, depressingly during the time Howard Mackie was writing Spider-man.
I use to get these packages of old comics, that they sold at the connivence store. It would usually have some really stupid issues, but some real good ones too. There where a few Avengers issues too. The first Avengers issue I read was #314 "Into the Void". I don't actually remember it being very good, as I was jumping into a confusing point. Those packages also had Avenger solo issues, featuring Hawkeye. It was all good, but it didn't grab me.
The next time I began reading the Avengers was during Kurt Busiek's run on the series, at issue #38 I believe. Alan Davis was drawing on art. I recall buying the issue because it had a marked down price of 1.99 (instead of 2.99, at the time) It was a great jumping on point, and held my attention of the series even through the unending horror of the Kang Dynasty story line. Geoff Johns took over the series after that, and soon enough Bendis was blowing the Avengers up.
The first Fantastic Four issue I read was issue #400. A shiny hologram cover no doubt enticed me to buy it. I can't imagine a worst time to try and read the FF - as Reed had just died, and Doctor Doom's Son (or something) was taking his place on the FF team. I found that very compelling, I gotta say. The rest of the story was very complicated, as it mixed in the Fantastic Force, and it simply all dovetailed into a very bad time to try and join the FF ranks.
The next time I tried the FF was because of the Animated series. I tried reading the Comic books, again repeating the same story.
The real time I actually jumped on the FF bandwagon, for good, was near the end of Chris Claremont's run on the series. There was a big storyline about Reed Richards getting stuck in Doctor Doom's armor. It was a rather confusing time, but it was all very fun. Jeph Loeb and Carlos Pacheco where an excellent follow up act
Again, the animated series drew me in. I read the corresponding comic book, retelling the same story. The next time I got into Iron Man was during Keron Grant's run on the book. I probably tried the series because of getting into the Avengers.
Thor vol 2 issue #32. It was a 100 Page Monster issue, with three issues worth of reprints. A great deal, and a wonderful introduction into Thor. I later used my knowledge of Thor in a Vikings Longship class I attended at school. I got very into the mythology. I also tried finding out the price of some beat up Thor issues my teacher had. They where in pretty bad shape, and probably would only sell for $7 or $8. So he actually said for me to keep them. I said I couldn't, but he said it was OK, so I took two out of the three issues. They aren't in prize condition, but I got the first Thor Annual (first appearance of Hercules) and Thor's first fight with Ego the living planet. This was a tremendous gift, to be able to read these actual issues, and I'll always be thankful for it. I continued reading Thor during a great but turbulent time, as Odin died and Thor became Lord of Asgard.
The first issue of Daredevil I got was issue #13. Having seen the Spider-man Animated series, I decided to give this issue a try, because it had the Kingpin floating down dead in the water. It turned out to be a spectacular issue, and I wanted to get more. But this was, again, a horrible time to try and be a DD fan, as Joe Quesada was interrupted from the series when he was made Editor in Chief of Marvel. I didn't know that, and waited patiently for the next issue to come out. It wouldn't be for a long, long time. But it was well worth the wait, and Bendis' "Wake Up" story line was a new level of art for me. Before Bendis took over preeminently, there was another cool story arch where Daredevil had to protect his identity in court. The efforts he put into keeping his identity where wasted, though, as Bendis soon let the whole world know that Matt Murdock is Daredevil.
I believe I tried reading the Hulk because of his appearance in those first few Avengers issues I read. I began around the end of Paul Jenkin's run on the series. I'm repeating myself here - but it was a bad time to jump in, and there was already a long plot about the Hulk dying of a terminal disease. I very much got into the Hulk, and got a ton of Peter David back issues. I simply loved the character. Bruce Jones, though not ending his Hulk run well, was a great read at the beginning when he took over after Jenkins.
I avoid the Ultimate series like a plague. I knew they where making good content, that it was very popular, but I refused to try it because I was so stuck in the idea that changing continuity was inherently bad. That was simply my opinion at the time. I believe I finally tried an issue with Ultimate Spider-man's first Annual, where Peter and Kitty Pryde date for the first time. It was a wonderful issue, and I quickly became a great fan of the Ultimate series. I began with Spider-man, then slowly got into Ultimates - X-Men, FF, everything. I recall saying to guy who ran the comic store thanks for getting me into the series, as I was able to get a bunch of back issues there. He said I got into those series myself - and I was quite proud of trying thing new thing, and finding it so good.