I voted "The songs he writes on his own" because his best tracks in my opinion are self penned (Billie Jean, Who Is It, Hollywood Tonight, Stranger in Moscow, TDCAU...), but it's all three actually. Because you have brilliant co-written songs (Remember The Time, Ghosts, Blood on the Dance Floor, We Are The World) and songs he didn't write at all (Lady In My Life, Human Nature, Butterflies...). He had the best in all three categories.