I've just started collecting and putting my Chaos Marines together. Originally I was thinking about going with an extremely Undivided army, but some of the god-specific stuff is starting to look pretty appealing. Unfortunately I only have so much money to put into this army, and I don't want to strain the limits of my friends' tolerance of "counts as."
I generally don't play in tournaments, so I'm not too worried about that. As for the armies I'll be playing against, one friend has Space Marines and Orks, one has Eldar and Tyranids, one has Space Wolves and Tyranids, one has Blood Angels, one has just Orks and one just has Imperial Guard. Another friend is going to get Necrons as soon as he has some money to spend on it. I'm generally the only Chaos player--I figured someone has to do it--but I also have Daemons, if we try to get someone into Warhammer and they need an army.
I know this is a pretty varied list of armies, but I'm trying to decide what would be the best investment for playing against them--regular Chaos Marines, Plague Marines or decked out Noise Marines?