I actually like skeletons more usually, with some exceptions. This mainly has to do with the fact that most zombies can't hinder other creatures due to Pest, and that's important for making sure the Necro can keep his distance while he summons and Meditates. Creatures that actually hinder also have good synergy with Cloak of Shadows, an equip which is incredibly important to the Necro.
Skeletons are also more efficient vs Nonliving creatures, which are harder for the Necro to interact with in terms of his Plaguemaster ability. Against Living creatures, though, zombies are more efficient, at least in terms of dice.
Skeles also have access to powerful Soldier-specific cards like Armory, Flank Attack, Garrison/Archer outposts, etc. Zombies have stronger support in-school, since cards like Rise Again, that Ziggurat thing, and Animate Dead only really shine in zombie builds.
Some conjurations meant for defense/late game also have the skeleton subtype, and benefit from Reassemble and Unholy Resurgence.
Overall, I'd say they're pretty equal. Playstyle-wise, Zombies are more efficient offensively while Skeletons are more efficient defensively, given the current card pool. When I play 10-channeling mages, I naturally tend to aim towards the lategame where I can probably overwhelm my opponent with mana and actions, so I like skeles more. However, I also have to prop up my offensive capabilities in the matchups against mages who can be even more lategame-oriented.
Before FiF came out, I often found room for Shaggoth-Zora in every Necro book I made. It doesn't have Pest and doesn't need much support besides a couple Crawlers to munch on to get big. A single Ichthellid is good too, since it is its own engine given how the ability and Plaguemaster works.
