Need PVP!

Hello, Im a newbie xbox 360 owner and Im looking for some awesome PVP games!

Im already planning on buying CoD4 or CoD5, which do you think I should go for? I like CoD4 cuz its modern, but CoD5 is kind of the succesor of the game and it feels wrong buying the old game in the series, if you know what I mean?

And besides the fps pvp action I would also like something like rpg or action adventure style? Im currently playing WAR on pc and I love the pvp in that game, so I would like to get the same experience on the xbox.

So should I go for CoD4 or CoD5? and does anyone have any suggestions on a game that can satisfy my pvp needs in a fantasy RPG or action adventure genre? Im not much into SP.

Thanks in advance!

I finally went down to my local EBgames and bought CoD5 since its only 50kr (6,5$) more expensive than CoD4, and I have had my share of time in CoD4 on my pc. Played until 4th mission and so far CoD4 SP was much better, but it all comes down to MP.

Anyways, no1 has any suggestions on some other competative game besides fps and racing? (I hate racing games)