Call of Duty... 4...5... or both?

Idk a simple question to anyone out there who plays Call of Duty... I am hoping to get a PS3 for Xmas and am only asking for GTA 4 with it because I know I will like that game. I would like to try out other games and for some reason Call of Duty seems like a good choice. But which one? I hear that 4 is plain kick ass and the online is amazing. Then I hear World at War is still really good but is somewhat disapointing for a "sequal'

Both look like good games really, but will tons of people still be playing #4 online in stuff in the next several months? And is World at War's online still fun? Any suggestions would be cool.

EDIT: Making a little poll for myself here based on the responses Iv'e gotten.

Call of Duty 4: Modern Warfare- 4

Call of Duty 5: World at War- 4

Both: 2

(Iv'e decided I just need to try both and see how it's like, but suggestions and all are still needed)

thanks, everything said helps. idk if it will help but im downloading a demo of 4 right now and im guessing they also have one of 5. It's going to take about 2 and a half hours to download this lol.

They are both great games, would you like modern weapons and setting or World War II?

The gameplay (online) is identical.

COD 5 is not really a sequel and its not really COD 5.

Ever since I got WAW I have not played COD 4.

well it seems like every PS3 game (the good ones) are either shooting\blowing crap up or racing..SoNin360

not Little Big Planet or Assasins Creed,god of war 3 probably wont be a shooter eitheir

well it seems like every PS3 game (the good ones) are either shooting\blowing crap up or racing..SoNin360