Which game do you prefer for online play and what platform do you like to play on?

I prefer Modern Warfare. To be honest, WaW did not really appeal to me so much, getting sick of the WW2 theme, there has been enough FPS based on that, at least Infinity Ward didn't produce it so therefore I wasn't too angry. But the good news the next COD installment will be produced by Infinity Ward again and its based on Modern Warfare again which is good news.

I use a PC to play this game by the way.

I voted for COD:MW on the PC.
COD4 was one of my most played MP games of all time, second perhaps only to Day of Defeat (the original).
I don't own consoles and I haven't played COD:WAW. I don't think I have the strength to play another WW-II shooter.

ditto

it took me awhile to get use to WaW but its not soo bad now... and yes Modern Warfare 2 scheduled late 2009

Call of Duty World at War is mine but then again I have just got my new PC and haven't gotten to play the CoD4 the full game only the Demo.
And even that is great.
The Only thing I Don't Like about COD:WAW is it is really buggy

The WW2 genre is tired these days. Give it a break for a while and then go back to it. Modern Warfare is the right genre for me!

Ditto!

I like COD4 for the lengthy single-player.
I like CoDWaW for the co-op.

like to throw in.... the next COD is going back to Modern Warefare

Call Of Duty Modern Warfare 2

For me, Modern Warfare. Ive been Playing World War 1&2 themed games for a while now (CoD2, Medal of Honor series etc...), so in campaign it was nice to be able to pick up a stinger launcher and wreak havoc, not to mention being able to use laser sights on guns, and being able to operate the turret of an aircraft.

Multiplayer was fantastic too, with the previously mentioned laser sights, and a diverse range of weapons i hadn't used before.

CoD4 brought with it an array of new things, whereas 5 had much of the same stuff.

Edit:

Awesome as! Cant wait.