Kinda easy being a Wych Cult enthusiest what I'd prefer but I think it boils down to (for me) in an "all-comers" list is the wyches - their extra benefits of drugs, wych weapons, 2 blasters, plasma and even their initiative makes make them hard to beat.
Wych Cult "Troop" load out:
6x Wyches, WW, Plasma, 2 Blasters, Succubus, Agoniser, pistol plasma and goblet on a raider
Kabal list with 2 wych squads or less:
8x Wyches, WW, Plasma, 2 Blasters, Succubus, Agoniser, pistol plasma and goblet on a raider
As for Incubi, they are fantastic in a Marine dominant environment but when facing Tau or Orks or non-marines they become overkill in some situations and/or harder to manage the right target for them.
Wyches, on the other hand, work in the opposite way in my line of thinking - if the target is tough for a squad of wyches then throw in another (that is why my wych cult load-outs have fewer wyches per squad). I have found that its not the number of wyches in a squad that wins a fight but the number of agonisers in the fight that makes you win.
Incubi are nice too - I am not playing Kabal as much.