The best Decompiler

The question you need to answer is: What do you want then decompiled to?

If you want assembly then there are many good ones, but if you want a higher language like C then my experience is there are no good ones!

Also, note that this is illegal in many countries. . .

I'm expert on computer forensics and infoSec. Due to ethical issues I can't help you unless I'm sure of your intentions, sorry.

Take care