Super Muties, they remind me of Orks from W40k
I love rampaging the Capitol Building with my companion.
EDIT: I chose them because Deathclaws suck :v
They're too easy, just keep on running backwards and shoot them and they'll just die easily.
I had to vote for the mirelurks, especially the king.
I am lvl 20 and can kill ANYTHING, yet a mirelurk completely destroys me before i can kill it. (Note: i dont use snipers, im more of a close-up shotgun person)