Which is the Greatest Dectective out of these three: Batman, L, or Sherlock Holmes?

Pretty much this.
Batman was initially promoted as a detective type. Unlike other superhero comics, from my experience (which is actually not that much), Batman's are more mystery oriented.
Just because he's a superhero, he can't be a detective?
I still think Sherlock Holmes is the better detective, but to not count Batman as one isn't right.
Oh and we were talking about Sherlock Holmes in a course of mine yesterday. We came to conclude that he wasn't that deductive so much as inductive. In other words, a good number of things he figured out, he was just lucky to be right.

Spoiler

If you're referring to when Darkseid used his Omega Sanction on Batman, it was shown that Batman was sent to another time and the roasted body was one of the Batman clones. So...Batman's the only one that didn't die.