I haven't really thought this through in terms if Minecraft mechanics, but these two are my #1 go to whenever I play an MMO. The summoner class allows you to summon a type of familiar, either getting stronger or replaced by a stronger animal the higher your level goes. Necromancer is also like this, in the way that it can summon and control the undead. Having classes that relies on the things that they can summon and create is an awesome feeling to me; being able to create your own personal army or animal bond.