Bah. ABC is the only appropriate answer.
Hard to narrow it down. I think Billie Jean, all things considered. Also, and I don’t care who makes fun of me, I really like We Are The World – of course that wasn’t just MJ.
When I taught in China, the kids all really loved “Heal the World”, which we translated into Chinese for them.
I have good memories of the kids there singing it and though it’s cheesy, it is nice.
I guess I’ll be the first to say “Human Nature”. Just something about the song and tune and lyrics made it a favorite for me most of my life.
Although “Man in the Mirror” is a close second.
My favorite is Remember The Time. Every time I hear it, I marvel over what a great song it is.
P.Y.T. came out when I was about 19 and *was * a p.y.t. and man, it brings back some good times when I hear it.
The Way You Make Me Feel
There are too many for me to pick just one. For instance, I’m listening to the Jackson/Paul McCartney duet “Say Say Say” right now, and must say it’s one of my favorites. Many of the other songs people are listing are equally good, however.
I guess I’m kind of like Michael Bolton in Office Space. When asked what his favorite Michael Bolton song was, he replied that he liked them all equally. 
The one that’s been going through my head all day is “Rock With You”.
Yes! Yes! Yes!
I just have to say I want you back. I’m sorry, but it’s Motown and I can’t say no to that. Also it’s a fantastic song.
I agree that Remember the time is a very solid song under the radar. I was very glad when Kris Allen sang it in Idol.
Billie Jean is his best crafted song, and Thriller is the most fun, but my personal favorite is P.Y.T..
Solo, Motown: “One Day in Your Life”
Solo, CBS/Epic: “Human Nature”
With the J5: “Skywriter”
With The Jacksons: “Blame it on the Boogie”
i’ll have to go with Human Nature and Dirty Diana, and i can’t decide which is number one.
I wouldn’t claim to say any one is “best” but my favorite is “Ben” too. I was a big Jackson 5 fan. I never paid a lot of attention to his adult work. I thought the video to “Thriller” was stupid, but I did like the video to “Billie Jean.” I had nothing against any of his music. I accepted that others considered he was at the least a near genius but it just wasn’t my kind of music. It’s like I accept the level of consideration for Caruso, or Maria Callas, or Judy Garland, or Dolly Parton, or Bob Dylan, etc. etc. and I may like one-off songs, but it’s just not my kind of music.
Just now, even though I was negative in the other thread, I spent about an hour watching videos. Surprising myself, I quite enjoyed “Thriller” this time, and several other songs, and shed some tears watching the Jackson 5 and his young solo work.
These were from the other thread.
Jackson 5 - “Who’s Loving You” (on the Ed Sullivan Show)
Michael solo - “I’ll Be There” acapella
I found these interesting things too:
Jackson 5 - Tribute to vocal groups (this is fun, from the Carol Burnett Show, the “Jackson 6” and later, “Jackson 7”)
Also from the Carol Burnett Show, this version of “ABC” is just about as corny as you could possibly imagine, but it turns really fun (it really does get to the song eventually).
The Jacksons - “Blame It On The Boogie” (this is laughably dated with the trail special effects, but it’s so much fun, and damn, Michael was sooo cute!)
This is the most horrific video and audio quality, but it’s my favorite “Rockin’ Robin.”
I haven’t found a video yet that wasn’t flooded with heartbroken fans. I’ve decided I’m going to stay out of the negative threads. People are hurting, and I feel bad for them.
I’m glad this thread is a celebration of his music and talent.
Top 3 in order
Off the Wall
Beat It
Thriller
Billie Jean is my absolute favorite, but Don’t Stop Til You Get Enough is wonderful as well. Just look at him in the video: there is such joy on his face and exhilaration in his voice. That’s the MJ I miss.
Man. I had forgotten what a good dancer he was.
Equipoise, thanks for those Carol Burnett links. The one with Janet is soooo cute. 
equpoise thanks for the video links.
With the version of Young Michael singing acapella, it makes me wonder if he would have done (if not won) on an American Idol.
Such raw talent.
MJ was never really my cup of tea. But this March 1983 performance of Billie Jean (from the Motown 25th anniversary celebration) has to rank as impressive. Among other distinctions, it’s said to be his first “moonwalk” performance.