Lokirfellheart wrote:I've decided I want a greater Daemon in my Daemons of chaos army but I cannot decide whether to get a Great Unclean One or a Keeper of Secrets. Any tips?
Great Unclean One with Balesword and Noxious Vapours fits more easily into standard Daemon lists because he fills a specific role (autokilling big things). He's also got a ton of wounds to make him more reliable against war machines. If you go with the Kipper, equip him with Torment Blade, Allure of Slaanesh, Siren Song and Soul Hunger but you'll also need to support him with the Masque and the Despair banner. Well, you might want those two things regardless of which
GD you choose but the Keeper specifically requires them if he intends to kill a Bloodthirster or a dragon.
Remember that a Greater Daemon can go through a block of infantry because he wins every round (tons of attacks + thunderstomp) and the enemy steadfast
LD can be modified by Daemons by up to minus 8 (Masque, Despair, D&D).
The standard 7th edition uber-setup (because it countered
BT and Kairos builds) is still reasonably good, and if you take the Kipper you should use the whole thing:
Keeper of Secrets, Allure of Slaanesh, Torment Blade, Soul Hunger, Siren Song
Herald of Tz, Lore of Death, Master of Sorcery, Winged, Great Icon of Despair
The Masque
The thing is, the Great Unclean One can be swapped into that combo just as well. He's relatively faster now than before because the
2D6" charge boosts him a bit, and he can beat blocks down even with the 4 S8 attacks because of the
D6 thunderstomp hits. He doesn't need big enemies to fail
LD tests in close combat because he's just going to destroy them with the Balesword anyway. Siren Song has been weakened because you can't be sure if the enemy you're forcing to charge you will reach you. Last edition when you saw an enemy flyer you could force it to charge you and you knew that with the 20" move it would reach you. Now, the enemy might just fail the charge and then the Keeper gets shot to bits by small missiles. True
los isn't a friend to 5 wound big creatures with nothing but 5+ ward saves. What does the Keeper do better than the
GuO then? Beat down small guys we don't care about in the first place since we have a ton of other guys for that too. Casualties being removed from the back is also a problem, because it means every
GD will take wounds from every combat regardless of the actual result.
I played Daemons throughout all of 7th and used Keeper and Bloodthirster builds. Now if I had to play a
GT with Daemons tomorrow, I'd either go without a Greater Daemon or with the Great Unclean One and use some 20 year old
GuO model that's ridiculously small and therefore hard to spot with true
los 
I have the Forgeworld Keeper of Secrets model and I'm not too happy about using her since she can be seen from miles away

It's too early to say which setup ends up being the most useful. It also depends a bit on whether named characters are allowed or not. Every Daemon build benefits from the Masque, but the Herald builds are probably a bit stronger than
GD builds when Skulltaker can be used.