[Drax]

it depends on what you want to do - Tzeentch obviously allows another power and improves the invulnerable save

unless you are specifically wishing to use Lash, then Slaanesh isn't worth it on the sorcerer - his initiattive without MoS is either going to be good enough as it is, or unlikely to be good enough even with the mark - thats just my opinion however

as for nurgle - i'm not too keen for a sorcerer.

so really if you can live without the improved save and weren't wanting the extra power, then you might as well not bother with the MoT