Uhh.. It seems to me that only obviously good ones are direct upgrades, like True Freeze or White Witches' (but, dat cooldown on the last one...). Yuyu is interesting, as hybrid units can theoretically provide more tactical flexibility. Adele's have me on the fence. On the one hand, AoE freeze. On the other hand, quite a bit less single-target damage and less up-time (and single-target magical damage is witches' niche)...
Rest of em... Not look very good to me, to be honest.