I liked 2001, 2002, 2003 and (the first half of) 2004 the best. But if I had to pick one, I'd say 2002, with 2003 a close-second.
I was really happy back then, young, in great shape, and financially secure. Not to say life isn't good now though, it was just a different time and I was going through a lot of positive changes then.
Highlights of 2002: Getting my first job, slimming down to 150lbs, attending an art program, getting an Xbox, seeing the first Spider-Man movie.
I remember back then I was into stuff like Cowboy Bebop, Invader Zim, Shenmue, Techtv, Toonami..