10. Creeper: he's annoying and he only drops gun powder which isn't very useful.
9. Zombie: He is annoying but very easy to kill.
8: Slime: He only drops slime balls... Not so useful honestly.
7: EnderDragon: drops egg for tomorrows breakfast :). Drops TONS of experience.
6. Skeleton: drops lots of good materials like bones for farming, and bows and arrows for killing.
5. Spider: Drops spider eyes for brewing. Also drops string for bows.
4. Chicken: Drops food that heals three hunger
3. Mushroom: drops meat and leather for armor and food.
2.Pig: drops pork chop that heals 4 hunger bars.
1. Cow: Very useful for food and leather. Cooked beef heals 4 hunger bars.
Hope you enjoyed tell me what other stuff to do EX. Mods, texture packs, mob facts. (etc)