Since my role as Con is to argue that Fluttershy is NOT the cutest pony, and since my opponent gave a very brief argument, I will counter by pointing out that Pinkie Pie becomes especially cute when she is in an especially happy mood, and of course the Cutie Mark Crusaders have oodles of cuteness thanks to their adorable quests to gain their cutie marks, and of course Twilight Sparkle must win special kudos in terms of cuteness in terms of the bigger episodes of MLP and the things she goes through (getting to a point where she initially faces Nightmare Moon and Discord in her final battles with them by herself before managing to get her friends with her via her capabilities, so to speak). I hope Pro will expand on his argument.
There is an episode, where the cutie mark crusaders mess up with the news paper, fluttershy is extremely cuter than all of them when she lays on her couch and cries harder than anypony and when she forgives them is cuter with her forgiving smile
The Cutie Mark Crusaders still however tend to outmatch Fluttershy for cuteness, especially during their debut episode where they are established where we find out the troubles Applebloom is especially is going through with the tormenting she is receiving and her adorable wish to just find out she's actually recognisably good at something. Likewise, there's also an episode where one of the Cutie Mark Crusaders is trying to help out Pinkie Pie with her baking of cupcakes and is absolutely adorable when she realises she's failed. Also, against Fluttershy there is the use of her "Stare" against her chickens, and pretty much anytime where she goes psycho crazy angry.
That only happened once with fluttershy when she went crazy angry, but that was because the animals of the canterlot garden wouldn't go towards her for some odd reason, in the first episode, fluttershy is extremely adorable when she meets twilight and spike, in the last episode of the third season, fluttershy is cuter than anypony can imagine when she starts trending the animals and singing in harmony with twilight
I present as counter evidence the episode "One Bad Apple", where the Cutie Mark Crusaders find themselves under attack from someone they thought was their friend, and how adorable and cute they are when they are trying to get Babs to stop, and then at the end the genuine heartwarming happiness they and Babs feel when Babs is officially inducted as their fourth member. We also have the episode where the CMC go camping with Rarity, Applejack and Rainbow Dash and we have Scootaloo's absolutely adorable attempts to impress Dash in light of her sheer admiration of her. Vote Con.