I don't know about it being the "best" typo, but my most embarrasing typo (and one which could have landed me in serious hot water) was when, after borrowing some programming reference books from a lady I work with, I sent her an e-mail in which I thanked her for letting me see her books... and mistyped the "k" in "books" as a "b".
Fortunately she saw the funny side of it, or I could have been in big trouble
.
My mind must have been on other things as I was typing the e-mail. Never a good idea.