Personally, I like Smithers, and the Comic Book Guy. However, the masses have spoken here.
Plato? Aristotle? Socrates? Morons!
~Only 18 more hours until I am hanging with Better Than Ezra!
Sideshow BOB!!!
But only because of his hair and that…that sound he makes…its so funny! And because I can imitate it so well that I made a teacher who overheard me doing it for my friends snort milk out his nose.
Euuuuuuhhuhuhuuuuuuuuhhhhhr…
I feel special now. Ahem. Yes.
I’ve seen all these quotes on the show, but out of all of them, only the Luigi ones make me laugh out loud. I don’t know why.
Anyway, I used to love Comic Book Guy until he got a little too popular. My favorite quote?
CBG: “I do not have to take this. I have a master’s degree in folklore and mythology!”
Professor Frink is, by far, the best character. Though Comic Book Guy and Bumblebee Man are up there too.
CBG: Do I detect a hint of sarcasm there?
Frink (looking at his sarcasm detector): Are you kidding? This things reading off the charts!
CBG: Oh, a sarcasm detector, that’s real useful.
Sarcasm detector explodes.
Gah! How did I miss that Sublight already used Homer’s brain? Here I thought I was being all clever. Hmph.
And third place of course goes to Sideshow Bob. How could it not?
Homer.
“Ooo! They have the Internet on computers now!”
'nuff said. 
My favorite character is Maggie. Her only line(as far as I know) was/is “Daddy”. Can’t explain it, except maybe the fact that she is not as innocent as the rest of the family things(when she shot Mr. Burns, and the look of hers when she sees the other baby, and the time she went out to search for Marge).
PD. Isn’t the comic book guy one of the smartest people of the town?
I would have to say Smithers, and Lisa, and Milhouse.
Worst thread ever.
I believe she also said “Daddily-doodilly” to Ned Flanders. And she is brave too. Remember when Burns dared the town to do something about his stealing sunlight. Everyone looked away but Maggie, she stared right at him.
Plus she looks really nice in the future.
I can’t believe no one said Senor Dingdong!
Bumblebee guy (also a good character) Ay-yiyai! Senor Dingdong!
Lisa: I thought you were just a marketing gimmick!
and at the end of that scene,
“Aw, stinking Chev-ay!”
DISCO STU!!!
“Disco Stu doesn’t advertise.”
YAY Kwyjibo!!! Finally someone stands up for my man Homer.
Come on! I know it’s popular to say that Homer is overrated, but really, his lines are funny in more ways than the vast majority of other characters.[I call the big one “bitey.”] The only one who holds a candle to him is Monty Burns. After Monty, Ralph, then the late, great Troy McClure.
Major character: Homer. He reminds me of my Dad, although Dad is usually much, much smarter. I say usually, because sometimes Dad tops Homer in spades.
Minor character: Comic Book Guy. I used to collect comic books, and I knew three guys who fit the profile. I also met Matt Groening in Los Angeles about 18 years ago at the comic book store of one of the three. Oh, and I am one of the models for Jason Fox in Foxtrot (the author is most of the composite however – only my more annoying features are incorporated.)
Marge’s Sister’s Iguana, Chub-Chub
Lessee, there are quite a few supporting characters that I like:
Puberty Boy – not sure if this character has a name, but you see him working at groceries, Krusty Burger, etc., and his voice is crackly. Utters the line “paper or plastic” to Marge’s sister Selma, then she starts to hit on him. He says “I’m sorry, but we’re not allowed to date the customers!”
Gill the Salesman – I think he’s the one working at Senor Ding Dong’s who always seems distressed “ohhhh, today’s the day of my evaluation from Senor Ding Dong!”
Comic Book Dude – I have a buddy a lot like this guy.
Herb Powell, Homer’s long lost millionaire brother. “I’ve soiled myself! How embarrasing.”
Lionel Hutz, attorney at law
Troy McClure
Nelson (the “ha ha!” boy)
The “arrgghh” Pirate guy
snip
I was going to say Homer, but I figured everybody loves Homer.(hey that sounds like another show I like.)
Homer quote: “I don’t know Marge, trying is the first step towards failure…”
“Sleep! That’s where I’m a Viking!”
Ralph Wiggum, hands down.
Gotta go with Lionel Hutz, attorney at law and jack-of-all-trades when the ambulances were having a slow week. Not gonna quote him as I don’t want to make any mistakes, but 80% of what he said was classic. We’ll sadly never hear from him (nor Troy McClure) again for obvious reasons… Ho hum, not to bring the frivolous thread down…
As for the core characters, Homer has to be the king:
Burns: “No no, Homer, use an open-faced club–a sand wedge!”
Homer: “Uhhh-huh-huhhh, open faced club sandwich…”
My favorite major character has got to be Mr. Burns. He’s so wonderfully evil. 
For minor characters, Comic Book Guy is right up there, but I think I might have to go with Kang and Kodos.
“They’ll make bigger boards and bigger nails. And soon, they will make a board with a nail so big it will destroy them all!”
I loved Hank Scorpio too, even though he was only in that one episode. I must have watched that episode fifty times, and I just never get tired of it.