Which Daemons to get?

[Blackcloud6]

My birthday is coming up and my wife wants to know what to get for me. I haven't really thought about it much, but I have an urge to start a Chaos Daemon Army after fighting a few of them in the last weeks. Now I have a pile of stuff that needs to be built for my Orks, Sisters, IG, Tau and Crimson Fists but I have no discipline and when the desire hits, I usually go off and buy what I want.

Now our group already has a Slaanesh army, this was the one I sort of preferred, we also have a Khorne spread out between two guys. So that leave Tzeentch and Nurgle. I'm leaning to Tzeentch. I 've got to decide today so the FNGS can put in the order tomorrow. So, what is cool and what is bad about these Armies? What should I do?

BTW, how do you pronounce Tzeentch; is it "Zen-itch" or one syllable with long Es as in Zeeeench?