I would much rather have a diabolical laugh as opposed to a maniacal one.
A lot of people throw these words around like they know what they mean. Well let me tell you something, you don't. No, you fucking don't. You use these words synonymously to mean "evil and scary" when in fact, neither word means "evil and scary".
The word "maniacal" stems from the word "maniac". Now, a maniac is someone who is silly, wacky or very serious on the dance floor. Is that the kind of intimidating, evil laughter you want? Do you want to verbally ejaculate a maniacal laugh in the face of your enemies, only to have them comment, "Boy, I bet he sure can cut a rug." No, you fucking don't. This type of laugh is more closely related to a small child laughing about something that really is funny only to it. God, I hate that. We get it, kid. Spongebob lives in a fucking pineapple. Stop laughing already.
Now, "diabolical," there's a laugh I can get behind. Diabolical's root word is actually El Diablo. Now an El Diablo is the devil, but not just any old devil, we're talking about The Latin Devil. The Latin Devil is much cooler than the Anglo-Devil, who does nothing but try and trick people into giving them their souls.
List of people that have outsmarted Anglo-Devil:
Dan'l Webster (wiki that shit, yo)
That Guy from Seventh Seal (I never saw it)
Anne Hathaway, etc., etc.
With all these people outsmarting Anglo-Devil, you have to wonder how he stays in business. I mean, Keanu Reeves for christ's sake? Do you want your laughter to sound like the guy that got beat by Keanu Reeves? No, you fucking don't. But The Latin Devil, do you know how many people beat him in a battle of wits? Zero, because El Diablo doesn't bother with that shit. He doesn't waste time with games of chess or courtrooms or being super-duper-hot like Elizabeth Hurley. No sir. The only thing he wastes is bitches, which in The Latin Devil's language sounds more like los bitches.
Play me to the desk.
PS - About five minutes after I posted this, I dictionary.com-ed "diabolical" and learned that the root word really IS "devil". This pisses me off.