What are the most used letters in the English alphabet?

In reverse order to avoid an unfortunate acronym:
3rd - a
2nd -t
1st - e

The gold and bronze medals are unsurprisingly but did not expect 't' to be up there on the winners rostrum. E is the champion in other languages, too. George Perec famously wrote a detective novel in French without an es (as it were) La Disparition (1969. This was then translated into English by Gilbert Adair as A Void - ingenius work in both cases, though the purpose escapes me.

For more than anyone needs to know about this topic see here.