Well, 5 is 4 with a WWII skin on it. Same multiplayer game engine and all. I can't say, I still have fun in 4, but I play 5 for the hell of it. If I seriously were to choose in life or death, I'd pick 4. 5 does have some guns I like though, the double barrel shot gun (modded mine, sawn off 
) I also like the STG-44 and Arisaka/ bayonet. It's just like COD4 with a WWII spin. Neither is really "better". Personally, I'd get 4, then 5.
You get the bayonet in COD5 though...
Edit: Me an my brother just got to 13
