Which do you think was the best Call of Duty game available on the 7th gen consoles, and what made it the best?

Well, it's easy to say the series peaked with CoD4: Modern Warfare, because that was the last game they truly made an effort to innovate, and every game since has just been an annual re-package/re-skin with minimal improvements, and almost all of those 'improvements' derived from modern trends.

That being said, my favourite before I stopped playing CoD for good was BlOps. Modern Wafare 2 was just a more refined version of CoD 4. World at War actually took some steps back with it's multiplayer, but brought in Zombie mode. BlOps felt like it had the best mix of everything-- Zombie mode, weapons, multiplayer game modes etc.

The games after that aren't even worth mentioning.

Modern Warfare followed by MW2. No contest

The first Modern Warfare. As far as I'm concerned the series decline started with Modern Warfare 2. That's where the series stopped trying to act like it was a realistic depiction of war and became a Michael Bay movie.

World at War. I really resonate with the WW2 theme to be honest.

CoD 2.

I ony played two call of duty games during 7th gen.
They were Call of Duty 3 on the Wii and Call of Duty Modern Warefare 2 on the 360 (which I only played the single player).
I remember almost nothing from Modern Warefare 2 but Call of Duty 3 was a great time. I really enjoy historical settings for first person shooters.

Black Ops. It was like MW2, which I liked a lot, but with better weapon balancing, less bugs, less hackers and less overly symmetrical maps. Series went downhill after that, with a brief upturn with Black Ops II.

I'm probably not qualified to answer that. I played CoD2, Modern Warfare, Blops 1&2, and Advanced Warfare (on PS4). None of the games before or after gave me that original Modern Warfare feeling.

Black Ops. It had an exciting campaign, fun multiplayer, and some of the best zombie maps (because it also had the original 4 lol). Each mode was jam packed with goodness.