You're actually asking me to choose? Hmm... Well i like this one:
Dean: "Did you bring quarters?"
Sam: "Dude, I'm not enabling your sick habit. You're like one of those sick lab rats that pushes the pleasure button instead of the food button until it dies."
Dean: "What are you talkin' about, I eat!"
But I love them all!!♥

LOL I like that quote too !!!

ummm i have many favourites, but this one is good:

Dean: "You broke into their e-mail accounts"?
Sam: "I used some skills that I happen to have to satisfy my curiosity".
Dean "Nice".

and

Dean: "Bitch"!
Sam: "Why did you call me a Bitch for"?
Dean: "You're suppose to say Jerk".
Sam: "What"!?
Dean: "Never mind"!!

LOL
also in the episode 'yellow fever' two of the best Dean quotes:

" That was Scary!" and "I'll man the flashlight"........

Dean: "Truth is, I'm tired, Sam. And, I don't know, it's like there's a light at the end of the tunnel".
Sam : "It's Hellfire, Dean".

Castiel: "It's not funny Dean the voice is telling me I'm nearly out of minutes"

That one cracked me up and

Dean: "Can I shoot her?"
Sam: "Not in public"

Dean: I'm batman.
Sam: ya ur batman.
Lol
and
dean: what?
Sam: I lost my shoe.
I love them
oh nd I love this one

Sam: I think she is siren. And I had sex with her.
Dean: oh man!!! Wats with u bangin monsters

This one is my fave.

Sam: What Dad "wants" doesn't matter!
Dean: You see that? That attitude there? That's why I always got the extra cookie. Ha Ha LOL!!

And here's another one:
[Sam trips and falls]
Dean: Wow, you suck!

lol i love that

Dean: dude, i think that he witch just gave you the clap.
lol and
Dean: Driver Picks the Music, Shot gun shuts his cake hole.
lol and
all time fave
Bobby: you idgets.

dean: nobody kill any virgins!

Harddd! I totally love them all but I think I'm gonna go with:

Sam: "Hey, Check That Out."

Dean: "Yeah, It's Close To Halloween."

Sam: "Remember Cinderella? ...With the pumpkin that turns into a couch and the mice that become horses ."

Dean Makes A Confused Face

Dean: "Dude, Could You Be More Gay?."

Sam Thinks about Dean's question.

Dean: "Don't Answer That."

and the awesome

Dean:"Don't objectify me"!!

I LOVE THESE

Dean: so you found some beetles, in a hole, that's shocking sam !!!

Dean: collage boy thinks he's so smart

Sam: What were you thinking shooting Casper in the face you freak

THESE ARE ALL FROM SEASON 1 THOUGH

Castiel:Hey ass-butt lol
Cas is so funny

Castiel and Zachariah appear in the beautiful room.
Dean: Suite Life of Zack and Cas!
Zach/Cas: ...
Dean: It's a... nervermind.

***

Dean: I hope your apple pie is freakin' worth it!

***

Sam: Yeah, what do you wanna do, poke her with a stick?
Dean nods
Sam: Dude, you're not gonna poke her with a stick?

***
My favorite overall:

Henrickssen: You think you're funny!?
Dean: I think I'm adorable.

***

And so much more!

LMABO!!!!

some of my faves...

Dean: Blow Me, Cas!

Castiel: I found a liquor store, and I drank it.

Sam: When I told Dad I was afraid of the thing in my closet, he gave me a .45



so many more...just the first couple that came to mind!!
and this is how real bros act!!!