The classic:
* "She sells seashells by the seashore. The shells she sells are seashells, I'm sure. So if she sells seashells on the seashore, then I'm sure she sells seashore shells."
This one is tricky due to the repetition of similar sounds and the length of the sentence.
Others that are frequently cited:
* "Peter Piper picked a peck of pickled peppers. A peck of pickled peppers Peter Piper picked. If Peter Piper picked a peck of pickled peppers, where's the peck of pickled peppers Peter Piper picked?" - This one uses alliteration and a lot of similar sounds.
* "Betty Botter bought some butter, but the butter Betty Botter bought was bitter, so Betty Botter bought some better butter to make the bitter butter better." - This one is tricky because of the repetition of "butter" and the changing vowel sounds within the word.
* "The sixth sick sheik's sixth sheep's sick." - This one is short but challenging due to the repetition of "s" and "th" sounds.
* "Busy as a bee." - This one might seem simple, but try saying it ten times fast!
Ultimately, the toughest tongue twister for you depends on your individual speaking habits and the sounds you find difficult to articulate.