If you used to use your Archon as a beatstick, the Succubus is the preferred choice, as her glaive gives AP2, the archon has no AP2 options.
Unfortunately, she can't take the Shadowfield, so only gets 4++, but doesn't lose it if it shorts out.
Wyches DO suck (Boo, my favourite unit in the fluff!)
All the coven stuff got better this codex, especially if you get the Coven expansion. Grots in particular are awesome now; I preferred them as my Archon retinue in 5th, they are even better now, so my Succubus is happy!