They want mob rule of looks and location, not necessarily utility. I wouldn't want the masses to choose a mob that has a high number of farming abilities.
To make a full informed decision, we would need to know what they would drop, any special abilities, and how often they would spawn. If they gave us that info, the mob with the best farming ability (ie drops) would be the winner. Doesn't make for a great vote.
I'd rather they just develop and release them. Mob A is just a squid with a tongue, Mob B and C would need extensive coding, Mob D would just be a reskinned blaze with higher hp. B & C are the only two that would require much work to get in the game.