I'm actually gonna say Halo. I know it's no longer the big name in shooters but most of my fun with online gaming has come from Halo. COD, Gears, or really any other shooter doesn't compare to the fun and holy s*** moments I get from Halo.
Destiny is all I really care about. The only next gen game I'm really pumped for, other than elder scrolls online. Once halo 5 details come out, I might get excited. As far as Titanfall, I have zero interest at this point lol. Doesn't really appeal to me.