I love 3, 4, and Reach, Here's why: Reach had the best armor.(I am still mad that you can not duel-wield...) I like 3 because the mark v looked really cool, and it had the SMG, and duel-wielding. And 4 has the best costomization, it has loadouts you can make and keep in matchmaking.(I still wish it had the mark v....)
Halo 1 is my favourite. I played it from about a year it came out up until Halo Reach was released. I know Halo 2 is my least favourite. The rest are somewhere between the two. I just can't rank them that easily, especially when one of them is part of a completely different video game genre. Still I love all of them.
i stopped at halo 3. at the end they gave some message about it being the last game and thanks for playing. then we seen some spin-offs which were annoying but were expected. now they are releasing halo 4...what happened to last game?
so i stopped at 3. if you say its the last i dont care what you do i'll treat it as if it was. so they'd have to do some pretty spectacular to get me playing again. halo was great but i think i'll have to go with halo 2. the duel-weilding and level design was great.