Oh, there are so many! As others have said, “Superstition” is tops. And “For Once In My Life”. I’ll also add (since it hasn’t appeared otherwise yet) “Isn’t She Lovely?” It always makes me smile, even more so since I found out it was about his daughter as a baby.
Favorite Stevie Wonder single? Though there are many worthy contenders, I gotta go with “Sir Duke.” From the opening fanfare, this is one of the all-time great feel-good records.
Honorable mention for a mellower tune goes to the underrated “Overjoyed.”
Sorry about the coma.
Aww, no love for “My eyes don’t cry no more” at all? The definitive hustle song, at least round these parts.
Superstition. I don’t care if it’s already been mentioned; Superstition wails. Also Sir Duke.
'pasttime Paradise" and “I Beleive”
“As” and “You and I”
Another vote for “I Wish”. When I was a young teen, I’m sure that I would have voted for “Sir Duke”.
I find myself unable to pick between the following
Boogie On Reggae Woman
As
Superstition
28 posts and no love for “Don’t Drive Drunk”? (Youtube link)
Seriously, “Higher Ground”.
Do I Do is the best damned piece of music ever written by anybody. Any suggestion to the contrary simply is not true.
Sez me, wit’ 35+ years experience of listening to Stevie Wonder. 
Overjoyed is probably his best.
Stevie’s one of those artists who is really good when he’s good…and not when he’s not. For example:
Yes:
Fingertips Part II
Send One Your Love
Isn’t She Lovely
Superstition
I Wish
My Cherie Amour
No:
I just called to say I love you
Sir Duke
Ebony and Ivory
Both Stevie and Paul are (at their best) musical geniuses who have, alas, turned out a certain amount of sappy schlock.
Yepp. I came in here just to say “Superstition”.
It was amazing. He played for almost three hours and did 30 songs. Almost all of his hits.
I’d have to vote for Higher Ground as my favorite.
“If You Really Love Me” does it for me, hands down. It’s not so much that it was his best, but more because of the memories it evokes for me. Hearing that song brings me right back to being a little kid, riding in the back of the family '66 Plymouth station wagon on the way to some historical tourist spot for a summer vacation.
As Paul Simon said “I’d like to thank Stevie Wonder for not making an album this year.”
I can still feel, see, smell, remember every moment on Bayville’s beach, at night, a fire going. Wrapped around my brand new girlfriend, as Fingertips part ll played. Top Three Memory
Oh yeah, Superstition and Sir Duke. You Haven’t Done Nothin’ also makes the grade for me.
While I love Boogie On Reggae Woman, Superstition, Sir Duke and Master Blaster, gotta go with My Cheri Amor.
Anyone remember the SNL skit decades back when Eddie Murphy was playing a record exec, trying to teach a bad Stevie Wonder impersonator (played by Stevie himself) how to sing? Eddie would start “My Cheri Amor” and Stevie would follow, nasaly, badly. This happened a couple of times and then Stevie cut loose with his unbelivable voice. Sweet Jaysus, it gave me chills. Heh, then Eddie tells Stevie “It still sucks, man.” Bwhaaa.
Superstition is in my all-time top five, so that has to win. I just heard As yesterday for the first time and was really blown away. But I also have to mention To Know You Is To Love You- I’ve never heard the original and I’m still a huge fan.