For me,

KZ2 online has been amazing, but I haven't played R2 yet !

How badly will I be raped if I start now ?

It depends what your in the mood for. I prefer KZ2, but since its lacking Co-op and death match R2 does hold a special place in my heart :D.

its pretty good, i really enjoyed it.

but the best is Call of Duty, with Halo not far behind.

Hell no! I tried it and it can´t even compare with the awesomeness that is K2. This in Ps3, can´t say for x360, and for PC well, I don´t play much online on it, but I remember CS and BF1942 back in the days were awesome.

R2 awsome. Kz2 awsome, now MAG awsome. take your pic you'll love it all.

In my opinion its Modern Warfare 2, then Halo 3, then probably Resistance 2

Wow, thought I was the only one the that was crazy impressed by R2's online. It is the first game to ever get me into its online mode. I've tried other games like Halo, MW2, etc., and just didn't enjoy the online. Anyways, I love the coop mode in R2, amazing! Uncharted 2 is the second game to get me to play online, and now I would prob have to give best online to U2.

Is it the best no but it's a lot of fun and thats what a mutiplayer need's to be.

You said it!