Rarity is still best quote source.
Applejack is second best.
Applejack: "Well, howdy-doo, Miss Twahlaht, a pleasure makin' yer acquaintance. Ah'm Applejack. We here at Sweet Apple Acres sure do like makin' new friends!"
Rarity: "Oh my stars, DAH-LING! Whatever happened to your coiffure?"
Rarity: "Out of MY hair? What about YOUR hair?"
Applejack: "Ah dare ya to enter the next rodeo when it comes to town!"
Rarity: "I dare you
not to enter the next rodeo that comes to town!"
Applejack: "And that, mah friends, is what we call 'Git'n 'er done!'"
Rarity: "Oh, please promise you won't tell her I feel this way. Please, please, please please PLEEEEEEZE!"*
Rarity: "Good heavens, what is that smell?"
Rover: ~~~~~"Smeeeeeell?"~~~~~
Rarity: "Ah, mystery solved. It's your breath."
Rarity: "Whining? I am not whining. I am complaining. Do you want to hear whining? THIIIIIIS IIIIIS WHIIIINIIIIING!"
Rarity: "I-DEEEE-AAAAAAAAAAA!"
Applejack: "Gown? Shoot! Ah was just gonna wear mah old work duds!"
Rarity: "You can't possibly be serious, Applejack! You absolutely MUST wear formal attire!"
Applejack: "Hmm... Nah!"
Applejack: "So all you have to do is make a different, stunning, original, amazing outfit for one, two, three, four, five... plus yourself, six ponies? And lickety-split?"
Rarity: "Oh, Applejack! You make it sound as if it's going to be hard!"
Rarity: "You, sir, are the most uncharming prince I have ever met! In fact, the only thing royal about you is that you are a royal pain!"
Photo Finish is third best.
Bonus tracks:
Twilight Sparkle: "All the ponies in this town are ca-RAZY!"
Twilight Sparkle: "Well, that was kind of huffy!"
Fluttershy: "Huffy the magic dragon!"
Braeburn: "And here's where we have our wild west dances! And here's where we have our
mild west dances!"
Chief Thunderhooves: "It appears that Sheriff Silverstar and I have come to an agreement."
Sheriff Silverstar: "We have."
Chief Thunderhooves: "That was the worst performance we've ever seen!"
Steven Magnet: "My moustaaaaaaache!"
Pinkie Pie: "ThIiIs MaAaKeS mYyY vOoOiIiCe SoOoUuUnD sIiIlLyYy!"
Twist: "Wadt thobe thweetth? I've got thobe pepperbidt thtickth. I bade theb bythelf. They'll bake you thbiiiiile!"
Pinkie Pie: "Don't forget your party hat, Forgetty Forgetterson!"
Pinkie Pie: "Holy moly, that's a lotta holeys!"
Zecora: "Tales of crops and harvests consumed. / If these creatures are in Ponyville ... you're doomed!"
Hoity Toity: "Oh, those amateurish designs look like a piled-on mish-mash of everything but the kitchen sink!"
Pinkie Pie: "She'll become a crazy cat lady!"
Twilight Sparkle: "She only has one cat!"
Pinkie Pie: "Give her time!"
*Twilight Sparkle: "You have my word. Losing a friend's trust is the fastest way to lose a friend."
Pinkie Pie: "FOOOREVERRRRR!"