It's hard for me to choose between Rock With You, Off The Wall and Burn This Disco Out.
Rock With You is funky but smooth song, but Rod Temperton wrote Rock With You as an up tempo song. Michael slowed the pace of the song down to make it the smooth song we all know. Michael mentioned this in his 1988 autobiography Moonwalk. The up tempo version was supposed to have been included in the Off The Wall (Special Edition) in 2001.