I don't even know how to differentiate them, they're all the exact same thing. Which is fine with me, I enjoyed every campaign from the original to Ghosts, it's a breezy 5-6 hours every year. But I have no idea what my favorite would be. They're practically identical and melt together in my mind and nothing stands out, good or bad, any time I play through one. I guess I'd lean towards 2 or World at War because of the WW2 setting.