Evolve pits four against one, so that one has to be made pretty fearsome. 2K and Turtle Rock have announced the pre-order bonuses, which includes two ways to make your particular monster stand out.
The Monster Expansion Pack includes a Savage Goliath skin available at launch, and a yet-unrevealed new DLC monster character for free once it becomes available. While only one player is a monster, Evolve has several different monster classes to choose from. You can check out the official site for more info on where to pre-order, but generally it's the usual haunts.
Evolve is due this fall for PC, PlayStation 4, and Xbox One.