I'll consider you're not playing as a Lone Wolf. Necro/Geo is a weird combination to begin with, since your damage would be split between physical damage and magical damage. I'd suggest you choose one of both types, unless you're looking for a more support/debuffing build and leaving the damage to the rest of the party. If that's the case, summ might be a good choice, since it scales off solely from the summoning ability, meaning you can have any main attribute you want (even Int, but it's not mandatory). Also, you won't feel lack of damage for spending a few points in Memory instead of Int. A summoner/supp might need a bit of extra memory to have multiple buffs and summoning skills (I'd suggest even a dip in hydro just for the heal/armor restores. It works great to magically protect the Bone Widow).
Now, if you're Lone Wolf, it's super easy to get 10 summ fast, so you wouldn't be spreading too thin. Just keep in mind what sort of damage you mainly want to deal. Remember the Incarnate can deal both physical or magical damage, depending on where you cast it.
