Well i got a baneblade, 2 leman russ's and the vindcator all painted with one can of air. I would really recommend it, the one thing i get really bored doing is basecoats and now i could basecoat a whole army in an hour. If all you want is basecoats i would just go for a cheap one, say £10-20 but if you want to do camo it will cost you more.
Well, the Chaos Space Marines have the chaos gods on their side, while the Space Marines have Games Workshop on their's.
So one has the most corrupt, twisted and souless entities in existance helping them while the other gets the chaos gods.