What is the most hardest tongue twister to say?

Well, that depends :] mainly because some people can say them better than others, like... For instance, the easiest one for me -

"How much could a woochuck chuch if a woodchuck could chuck wood."

Where others might not be able to say that at all.

I can hardly do --

"She sells sea shells" {Mainly cause I have a lisp.} {{But I'm sure somebody else could say that alot better and easier then I can}}