Damnit... double post.
Right, may as well use the post space.
With the Chaos Space Marines, the key (and best thing from a hobbying perspective) is the almost extreme amount of customisation you can do with them, even with just the base plastics (though at last GW is releasing the MasterCrafted range, I think that's what it's called). And that's sort of what you're going for with them: individuality (and a good healthy/evil unhealthy depending on POV dose of psychosis).
The Daemons just look mad from the off and they're much harder to model (as far as new weapons, extra trophies etc. are concerned).
As for the actual playstyle, with Daemons, you take a risk that beginners shouldn't need to take (starting force on the table) and with the rest Deep Striking, you can end up being too cautious. The Space Marines can (with Drop Pods) do the same thing, only better. The CSM don't get this problem, it's just boots on the ground, yelling profanities and shooting bolts. The Troops choices are much more newby friendly and proxying is much easier (i.e. more viable - CSM/any other troops choice except Berserkers, CSM/Chosen, Terminators/Oblits, Daemon Prince/Greater Daemon sort of), but there's enough variation among the army list to keep you wondering.