Which Call of Duty game made so far do you think has the best single player campaign, and what's your reasoning as to why it's the best?

For me it was COD 4 but, I never played a COD game before that one so, my scope is limited.

Cod4
Call of duty 2 big red one (ps2)
Mw2
Infinite warfare
Black ops 1

In that order

Black Ops 1 for me. Never liked the plots of MW2 or MW3. Ghosts was ok, but generic. Advanced Warfare takes second for me.

And that is all I have played of the franchise really.

COD4
CODW@W
COD2

All the other ones went balls up crazy after COD4

Advanced Warfare > Black Ops 2 > Black Ops 1 > Infinite Warfare >Modern Warfare. Those are my top 5.

I much preferred the more realistic and grounded tone of COD 4 in comparison to the Michael Bay inspired craziness of later entries that I've played.

Black Ops 1. The plot is interesting as well as the ending twist, even if they're a bit silly and predictable. I really dig the setting, weapons, missions and set-pieces, and the characters were at the very least memorable.
The only Modern Warfare i finished was 2 and i was extremely bored halfway-through, and can't remember a single thing about it aside from "gotta stop World War 3, bruh".
Black Ops 2 had some nice parts as well, mainly the ones set in the past. I feel like they kinda botched the plot by trying to tie the past and future timelines, which are set almost 40 years apart, leaving many, many plot holes. Ofc nobody plays COD for plot but i feel like BLOPS 1 did try a bit more.
That's it, those are the only CODs i ever played.

Yeah I was gonna say pretty much the same thing, I'm replaying it now and it's nasty, unglorified portrayal of war as a hellish struggle just to survive gives it a lot more depth than its more action-movie-esque stablemates. It also doesn't get as carried away in over-the-top setpieces as later entries.

All that said, I think Black Ops II takes the #2 spot for me; though it's a much shallower game thematically, it's the only COD game I'd say actually has a good story, the branching narrative paths were a nice touch, and the near-future tech struck an admirable balance of being cool but still relatively grounded. Plus it was a sweet novelty to be able to play a COD game with both motion controls and pretty graphics. XD

Call of Duty 2.
Cull of Duty World at War.
Call of Duty.

I find they have the best pacing and story... Whilst not being only a couple hours long like Call of Duty 4: Modern Warfare.