Note: There are spoilers here, so you have been warned.
I Googled around to search for the best ending in Call of Duty: Black Ops II and having found not a lot of concrete information about achieving the best ending in Black Ops II I decided to play the game from beginning to end to see how to achieve this. Now this is the most minimal way to achieve the best ending after playing the whole game from beginning to end:
- You must successfully complete all four strike missions (this is to secure an alliance with the SDC). If you fail a strike mission once, do not worry. Generally you have 6 strike teams for you to play with, which means you have six chances to get it right. I only failed in "Second Chance" once.
- You must be able to save Karma, regardless whether you are able to do so in the mission, "Karma" or in the Strike Mission, "Second Chance" (that's when you fail to rescue Karma in the original mission and is actually the fifth optional strike mission)
- You must not kill Alex Mason. Now this is easier said than done because in the final part of the mission, "Suffer with me", Hudson and Noriega will try to trick you that the person in the hood is Raul Menendez when in fact it is not. Shooting the person in both knees (or anywhere other than the head) will save Alex Mason. It is possible to shoot Mason in the head, which will get you to what I called the "bittersweet" ending.
- Farid must survive (which means you have to kill Harper).
- As Menendez, you cannot kill Admiral Briggs (otherwise he will automatically kill Chloe Lynch, who is meant to help you crack the worm)
- You have to save the President of the United States (I think that's a core part of a mission)
- In the final mission, "Judgment Day", you cannot kill Raul Menendez
It is okay not to discover every clue within the campaign or burn Harper by accident (but you will not be able to find who the CIA traitor is until it is revealed to you). It is also not necessary to kill DeFalco (someone else will do it for you).
I played this campaign in Recruit (which is contrary to popular belief that you cannot achieve the best ending in Recruit).
Anyways, happy playing.
By the way, stay behind to finish watching the credits: you'll get a special surprise