Of the two I would go Daggerspell. That being said I would add the witchcraft purge ability to your Shroudmaster 17pt build for the amazing synergy that goes with Occultism's Stilness. It would give you an AOE Silence and Shackle.
The reason I would go Daggerspell is because of the surprise + damage that Shadowplay and Sorc have that Occultism and Shadowplay cannot compete with.

[CENTER][Linked Image from nodiatis.com][/CENTER]