Good Lord, ShankS ... want to help write the movie? :)

Yeah, if you're looking for efficiency, you'll have to bring the hammer down hard on the head ... cracking the skull and mushing the brain.

An interesting way to kill someone with a sledgehammer:

Loosen the head, so it's just sitting at the top of the handle. Hold one of their loved ones hostage at gunpoint, and tell the person they need to kill you efficiently with the hammer to save the loved one. When they raise the hammer over their head to bring it down on yours, the head will slide off and bonk them in the head. When they look at you stunned (if they're not unconcious), turn the gun on them and shoot.

Fuck all these goddamn "what's the best way to kill someone threads"

You wanna know the best way?

With a goddamn gun simple and effective.

i must admit, all the years, since a young age, I've had watching horror's, has kind of warped my mind into weird scenarios and ways people get killed. If you're after some input for the film, yeah I'd be happy to help out, give me a scene and i'll add some extra touches. ;)

Place the hammer next to the victim with the handle upright, put a foot on either side of the "sledge", grab the middle, and pogo-style allover them...?
Smashing their fingers one by one would be fun if you had the time.
Crushing the wrists an hips would have to be bad too...
How about - Stand above them, looking down, swinging the hammer in large arcs back and forth over their face, moving lower and lower until it takes their nose right off with it.

If you wanted to finish them, take the sledge off the handle, so you're just left with the big stick, knock them about the head, not hard enough to kill, but keep trying 'til they're knocked out...
Whilst they're "out", lay them on their back, and place the sledge-handle evenly in their mouths so it'll balance there for a while.
Get yourself a medium sized ladder, go to the top, and jump down being sure to plant a foot on either side of that handle on your way down - that would about do it.

Overhead chop into the crotch as they lay in front of you, spread-eagle.

If it is a guy: He dies in agony.

A girl: You sick S&M loving bastard! I hope you tip her well. (or she tips you...)

take the hammer to a pawn shop, trade it in for a knife, and then stab with the knife

Good Idea!