Halo 2 (First)
Halo (second)
Halo 3 (third)

I've played all of them alot during the last two years and I'd say:

Halo 2 - Very good campaign & multiplayer with good gameplay.
Halo 5 - Campaign story isn't the best, but gameplay and visuals are great. Very good multiplayer.

I don't know about the 3rd one. I haven't played much ODST but it was a solid campaign. Reach had an amazing story but maybe the worst gameplay. Halo 3 has a good campaign but that multiplayer is the worst. CE has grown on me after playing it more, some campaign levels are horrible though but multiplayer is good. I enjoyed Halo 4 campaign and it looks great, multiplayer was decent.

Halo 3
Halo Reach - (Game that gets too much hate. Solid campaign, amazing forge, and competitive MP post nsnb)
Halo CE (with Halo 2 closely behind) - Marvel of it's time, still the backtracking makes it lower on the list

2, 3, Reach, 1 , the other stuff

Reach just needed sprint to not be an optional skill...

1. Halo 3 (Consistently great in all aspects)
2. Halo: Reach (Great Story, Good Multiplayer, Awesome Forge)
3. Halo 5 (Meh Story, Great Multiplayer, Best Forge)

In terms of emotional story and gameplay mechanics, Halo Reach is my favorite. Followed by 2 and 3.

Though I've barely played 4, never played 5 or ost.

1. halo  <-- game me the awe I once had with mario 64 when i first saw it, plus the many late night to early morning lan parties with multiplayer.

2. halo 2 anniversary <-- just a great game done right with nice upgrade in graphics and sound.

3. Halo Reach <-- just loved the story and game play / Halo 3, just a great game and couldnt decide between the two.

others that come to mind:

I liked halo 4 , the environments went big again, but the special ops was the best part of it for me.

halo 5 <-- meh   the warden fight for i think it was 5 times is just kinda lazy and unimaginative.

The halo I cant stand or ever finish is ODST. i so hated this halo, nothing i liked about it and never finished.

Oh yeah dont forget Halo Arcade is coming out!! LOL   i was so mixed about this announcement.

Halo: CE
Halo: 5
Halo: Reach

Basically, CE is my favorite by a wide margin. It was the most significant game of my adult life, in terms of its impact on my love for gaming. I have a great memories of spending Thanksgiving weekend marathoning the campaign with my brother.

Beyond CE, I like all of the games. Halo 5 had the best multiplayer, IMO. So, I put it in second. After that, I just happen to remember Reach the most. So, I picked it for 3. They're all great games though.

Good to see Halo CE get such praise. Its amazing. Halo 3 is my favourite as it does everything right.

1. Halo 2: Was such a genre defining experience, and one of the biggest slap in the face I ever got in my gaming experience. Also it's kind of the kickstarter for online play.

2. Halo CE: I don't think anybody has forgotten the sense of wonder you feel when you first arrive on the Halo. Such an incredible experience. F**k the library though.

3. Halo Reach: Even though everybody knew the story of Reach, the story was told in such a way that it kept me invested from start to finish. Also, that ending, damn...