So if you go to Account and click Get My Data and open the file, a few lines down are shown the wins and losses you have with each class with which you can calculate your winrates (I prefer percentages).
An interesting contrast is between my Inq and Sorc winrates, 86% and 38%.
My second best winrate is with Paladin, 83% (I don’t know why this one is so high).
My worst is sadly with my favorite class, Possessor: 13%.