Anyone considering BJJ or sambo famous fighters has probably no experience in real combat whatsoever. Most of what's illegal on the UFC beats easily any lock or ground work.
Anywhore, best fighter of all times: Bruce Lee. Fast as a lightning, and a genius.
You realize that Bruce Lee never actually fought, right?
He was nothing more than an excellent technician/martial artist, and an actor. He was not a fighter.
Also, he was like 140 pounds. Jose Aldo would destroy Bruce Lee.
Having said that, Anderson Silva is indisputably the most dominant fighter with the most impressive record considering the ways he finishes fights and against whom.
Fedor also carries that same mantle minus his last few fights. Everybody gets to the point that they have seen better days.
GSP is great, but he is too much of a pussy to risk a loss and doesn't have the ability to absolute destroy people and finish the fight.
If Jon Jones moves to Heavyweight and continues his dominance, which I think he will not be as successful at heavyweight, he could become the greatest fighter.
For now, Anderson Silva is definitely "the best" fighter the world has ever seen.