So hard a question. I talk a lot of Champions, 4th Edition, but the fact is that I probably either played or ran that game for less than four years, basically while in college. I had the first edition of Champions and loved it, and didn't even know two more editions had come out when I hit the big blue book. I bought Fifth Edition, revised, which I hear is pretty good, but never played it. Even in those college years Champions was only off-and-on.
Now, in full disclosure, I ran Fourth Edition Dungeons & Dragons pretty consistently for almost five years straight: two years in Ohio and three years in Kansas. When that was done I ran Marvel Heroic Roleplaying for another year. Someone who knows me recently said that suffer from "Hobby ADHD" but that tends to be more my tendency to buy and talk about running games; in reality I've been pretty steady.
If you want to talk about what game I have really played the longest (in terms of starting and not stopping), it's the home-brewed ruleset that used at EOW, which I've been a part of for the better part of the last decade, but we only play it once a year.
I loved (and still love) Champions because it was the first universal system that I had found that emulated one of my favorite genres: superheroes, and I spent a lot of time putting to paper all the superhumans of my childhood daydreams.
4E worked, quite honestly, because it was easy. At a time when I had a lot of stuff going on in my life personally and professionally, it was simplicity itself to cobble together three encounters and know I'd have the makings for a fun evening. The fact that it would be light on roleplaying and more closely resemble a strategic boardgame didn't always matter.
And I will say this, for all my bitching about Marvel Heroic Roleplaying on this blog, I feel like it did a better job of capturing the genre of comic books better than other superhero RPG's out there. As I read somewhere, it was the first RPG that felt like it was a comic book RPG, not a superhero RPG. It was also one of my first big leaps into low-crunch "narrative" RPG's, and most of the group took to it pretty well. It's problem was that after a year, everything started feeling the same when it came to gameplay, the other side of the sword edge to its easy PC/NPC construction that also made it popular when it came to squeezing in game sessions into a busy schedule.
And frankly, I am not a huge fan of the EOW homegrown rules set. It's clunky and outdated and doesn't always make sense. It's very firearm-oriented, reflecting the bias of its creators and the "genetic root stock" RPG's that helped make it. It's really the sense of playing with people who have been friends for so long and who do genuinely love getting together to game that really generates the fondness I have for EOW.
On rare occasion here I talk about "Mi Gran Sueno" (or "My Great Dream"). It's a term that actually was given to me to describe something very off-topic for this blog, but sometimes I use it to describe what I would really like to do with my RPG hobby. I would love to run a campaign full of interesting places and characters, where the players can really get into the environment and interact. Someday I'll make that happen.
I suppose this is the long way of saying my favorite game is the one I'm playing, the one I'm enjoying now, in the moment. Roleplaying games are meant to be a hobby, something actively done, and any time I'm doing that, then the rules are doing their job.