Never played COD before but thinking about it

I've never played "Call of duty" before and am just back and forth about getting it but I'm not even sure where to start? which one to buy first? I'm mostly interested in multiplayer shooting rather than a solid campaign, however, having both would be great too? I don't really want the multiplayer servers to be dead either. I also heard that one of the COD games used to have a prop hunt mini-game and I really love that idea.

So basically, which one should I start with?