While not limited to WanChai, this poll/thread provides a few recommendations:
Your favorite club/bar/pub in Hong Kong ?
Imo, there are broadly three types of 'bars', not sure which type you're interested in:
a. drinking only plus perhaps a TV
b. with a dancefloor but
not a nightclub (e.g cover charge, no happy hour)
c. with a pool/billiards table or other diversions
For Wanchai, one might add a fourth category, e.g. those types of establishments where men encouraged to buy drinks for the staff ... but I doubt that this is scope of this post.