It depends on what you need and what you are looking for.
Asajj's mass dispel is of great help and she stuns! but she is reeeeally slow and... at least with gear 8 doesn't haver a very big health pool (never seen one with higher gear).
Savage is just a bruiser with lots and lots of hp who can deal a pretty nice damage when he crits, but he has nothing special (he doesn't scare me when I see him in arena/GW)
Ventress is great for debuff and stun within a night sister team including NSI and Daka. I have also added Talia and use them to run the first half of the GW.
Ventress is too slow and her AI is bugged/terrible. Savage is actually viable in arena and raids for his self buffs to waste the rancor's roar and Offense Down
I have both, but only use one of the two. Ventress is great fighting pigs in raids. Savage deals too little damage to really matter much.
Though I must say that if you do not have him already (or have Rex), you should also get Ackbar ready. He can do wonders against debuffs, in particular piggy captain death mark.
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Asajj's mass dispel is of great help and she stuns! but she is reeeeally slow and... at least with gear 8 doesn't haver a very big health pool (never seen one with higher gear).
Savage is just a bruiser with lots and lots of hp who can deal a pretty nice damage when he crits, but he has nothing special (he doesn't scare me when I see him in arena/GW)
Make Zader Great Again!
Though I must say that if you do not have him already (or have Rex), you should also get Ackbar ready. He can do wonders against debuffs, in particular piggy captain death mark.