IIRC the most frequently used letters in English text are, in order of frequency:
ETA OIN SHRDLU
Why do I have this factoid stuck in my head? Because I read that book "Gödel, Escher, Bach: an Eternal Golden Braid" while I was in college and, among many other things, Hofstadter loved to talk about ETA OIN SHRDLU.
I should get a copy of that and read it again, it blew my mind when I was young but I suspect it might seem a little quaint now. Then again, how can you learn about Gödel incompleteness without being amazed? And humbled, it sure is a check on the ego of young STEM enthusiasts who think they're learning how to solve everything.