I never played halo 2 But I have played halo 3 - odst - reach and I think 3 is the best out of those 3.
I can't tell you how many times i've played the campaigns and split screen matches in Halo 2 & Halo 3.. over and over! Man those where some good times.
If anyone says anything other than Halo 2 than **** you. The game revolutionized online shooters and gaming itself. There will be no other game that had the community halo 2 did. Not to sound like an oldfag or anything but its true.
Halo 2. It was surprisingly the first FPS I had ever played. I first played it at a LAN party and it was so much fun and I was just terrible. It was also the first game that I played on Xbox Live. My friend and I played a lot before Halo 3 came out and I got to level 15 in Team Slayer (I don't know if it was hard to get there or not since I was still a noob).
I don't understand why some people say Halo 3 is mediocre and not the best Halo. Its campaign was, by far, the best, its multiplayer was, unarguably, the best, it included custom maps and gametypes which added more replay value than anyone ever expected in a game. No other Halo has has, near, as much replay value.