What is the best weapon to kill a behemoth in fallout 3

the fatman, rocket launcher, any high damage weapon. you want to go all out on these guys Actually yes the fat man is good but still I killed it with the starting pistol. All you have to do is Start attacking it and it will follow you, then you go into a 2 story building, then just start attacking it with a rifle, pistol, on the looks of it you don't have very good weapons. You friend Dragon! :D