Hard to say now, for fun I dug through Total War stats/polls. Don't play it, but though it would be fun.
Not exactly indicative of WHFB playerbase but instead contemporary faction popularity.
Empire, Skaven, Lizards, High Elves skew popular.
Warriors of Chaos and Beastmen on bottom end of things.
One tasty poll was this one, with almost 12000 response it has quite the sample size. The relevant result is "I don't play this race" https://docs.google.com/forms/d/e/1FAIpQLScJjhszdgfENi29-jsuXqk9sYyO_RhMTX_wQcNPeu6o5RQuvQ/viewanalytics
9% I don't play this faction for Empire versus 66% for Beastmen. Ouch.