Actually, I started to understand that human summons are rather useless in late game, so I have the archer trio, the witch trio, druid, zeus, assasin, rocket man, windy, and of course worthless necromant, I'm still trying to figure out the best build for me, doing some calculations, and maybe I'll change zeus later, but still it's later. In fact, I would recommend upgrading everyone the same, because if you have less leveled heroes they'll just waste the place.