Binders really begin to come into their own at 8th level and above, once they can bind 2 vestiges at once.
Also, as mentioned before, Dread Necromancer's shtick starts at 8th level.
I'm also going to be "That Guy" who say straight druid.
At 8th level; you gain access to Large size for Wild Shape, have 3 wildshapes per day, got 4th level spells...