Battlefield 4, mostly because that's the one that I actually own out of the 3.
However, it depends on a) the styl of game you play, and b) whether your hardware can provide an enjoyable playing experience without needing to be upgraded.
For example, I still play Halo: CE (which runs extremely well on my current system -- no surprise, since it ran well on my old Windows XP system); I like FPS games, which is why my game library also includes classics like Quake 1-3, Unreal Tournament (GotY, 2003 & 2004 versions), Halo: CE, Halo 2, & BF3 & 4 (plus CoD: World at War on my Wii). But I also like RTS games, like Age of Empires I, II & III, Starcraft (original/Brood War), Starcraft 2, MechCommander 1 & 2, Civilization III & V, Star Wars: Rebellion, & Sid Meier's Alpha Centauri; RPG games like Diablo & Diablo II; and flight sims like Combat Flight Simulator 1 & 2, & MechWarrior 4.
So, if fantasy settings appeal to you more, go for Shadows of Mordor. If you prefer sci-fi & futuristic weapons/combat, go for Crysis. If you prefer realistic weapons & combat, go for BF4.