Personally I play Cryo 3, Sorc 3 and Necro 3.
Necro:
Max Skeletons, Shoggoth, tower
Dirty Pole to 32 duration.
Level 10 Flesh Hoop so that each hit gives you 10 stacks of Necromancer Bane
1 Level Flesh Cannon for range refresh on boss monsters
1 Level Gather Corpse
1 Level Disinter
Rest of points can go into like Flesh Cannon or whatever you want really.
Sorc:
15 Summoning
1 Summon Familiar
Max Desmo
Max Evocation
Summon Servant max (though it really depends how much you want and need this, I would only spend the money for the mats for raids or maybe a group challenge mode)
Max Morph
Max Riding
Max Hold (kinda of a taste thing, depends on if you want another command for your demon or not)
~12 Salmion (His heal depends on his own hp, therefore leveling him up increases the heal he does, the debuffs he does also can be okay)
Rest of points where you want
Cryo:
1 Ice bolt
1 Ice Pike
15 Ice Wall
Max Snow Rolling
Max Sub Zero Shield
Max Frost Tree
Rest of points into Ice Pike
Generally I apply the Necromancer debuff with Flesh Hoop even in a group of enemies as I can simply freeze them. You can roughly circle through 3 x Ice Pike and 1 Frost Tree with just a little downtime, thus rendering a big amount of enemies useless. As enemies are frozen they can’t attack while you can apply Necromancer bane either with Hoop or with Flesh Cannon. Hoop also has “Attack Weakened” as well which reduces the damage you and minions take slightly.
Of course there are a lot of attributes to max in all 3 classes.
Not sure what I will do after Re:Build. The current build I have has a lot of defensive options but getting Bokor could be amazing as well though you need to change how you play as you loose the defensive options.