Witchcraft summons and Geomancer, are best and most in that order.
All the other schools can only sumon an elemental and they are sort of weak.
Spider and Armred undead Decapitator are my go to summons spells, bloodswarm is also kinda weak.
I load my fighter up with summon scrolls so I can have the most summons available for a party, but usually instead of summoning, I get the mage to buff the fighter, he is usually a better investment if built well and buffed heavily than any other summons.
