They've both got the same basic gameplay, but I'd take CoD4 because the campaign story's miles better in my opinion. I mean, CoD5 does things in the WWII setting that are very good and enjoyable, but CoD4 does a lot more in a slightly more original setting.
As for multiplayer, they're practically identical. Both games have just about the same number of players online so there'll be no trouble finding a match - it comes down to if you'd rather play with weapons from today or weapons from 1940.
As for multiplayer, they're practically identical. Both games have just about the same number of players online so there'll be no trouble finding a match - it comes down to if you'd rather play with weapons from today or weapons from 1940.