I love Invincible and listen to it often, but Dangerous - it's the absolute top, from the sound of the breaking glass to the very end.
I wanted to make song-to-song comparison, but I didn't get very far:
Unbreakable ~ Can't Let Her Get Away
Heartbreaker ~ In the Closet
Invincible ~ She Drives Me Wild
I mean, (EDIT: not only) ballads on Invincible are great, but songs like Will You Be There, Black Or White, Heal the World, Give In To Me, Gone Too Soon, Remember The Time are uncomparable to anything else...
I love individual songs on Invincible ("Unbreakable", "Threatened", "Heaven Can Wait") but I will admit that it's less cohesive as an album than Dangerous by far. Dangerous has a single feel to its tracks across the board and Invincible doesn't really have that -- it has a sort of "justified pissed-off-ish-ness" vibe at the first three tracks and then at the final track but beyond that it's all over the place.