It's a draw between 2008 and 2016
Both years have incredibly high-highs
2008 = Iron Man, The Dark Knight
2016 = Civil War, Dr Strange.
But also some low lows
2008 = the Spirit (aaaaaaghhhh !) , Wanted
2016 = Batman v Superman, Suicide Squad (and those are pretty ****ing dire ! Which is a lot coming from a hard core DC fan like me !)
I suppose 2016 gets the edge by also having Deadpool ( which I enjoyed,and thought was good) and X-Men Apocalypse (which I enjoyed but thought was kind of mediocre).
2008 had the Incredible Hulk (kind of mediocre, but mildly entertaining) and Hellboy II (which wasn't bad IMO).
Honourable mention to 2014 , for having DOFP (which was pretty good, but forgettable) Winter Solider (which is great) and GOTG (which I loved, and in my top 3 all time cbms) although it also had ASM2 (yuck !) and TMNT ( barf !).