Sith or Nightsisters

Really not sure which way to go. Yes I am kinda scatterbrained. Would it be better to work on Nightsisters or Sith.

My collection is here: https://swgoh.gg/u/ziglet/collection/

Nightsisters: https://swgoh.gg/u/ziglet/collection/?f=nightsister
*no Zeta yet

Sith: https://swgoh.gg/u/ziglet/collection/?f=sith
*Zader leadership, Nihilus Unique zeta