5994991
Does it need to be pony?

Out of all fics I ever read during my time here, it's either Setting Her Heart Aflutter or Let the Silence Sing.

5994991
Hearth's Warming Wishes is adorable if you like Fluttercord, and i've been told my fic Dodging Bullets is cute. there's more, but i can't think of 'em right now.

5995088
Yes. Anthro/humanized pony is also ok, but pony is preferred.

I've found Of Lilies and Chestnuts to be heartwarming. One of my favorites.

The cutest fic I've read is something from the Naughty folder: "After Hours" by Rinnaul. It's about a teenage Scootaloo and Rumble, losing their virginity to each-other. And yes, it has sex in it. But (unlike most sex fics) it's not meant to arouse the reader. It's pure adorableness!

A not too distant second, is "Colts Will Be Colts" by Trick Question. Scootaloo's grown up a bit, she's a 6th grader. And a younger kid is a huge fan of her, he thinks she's the coolest kid in school. Scootaloo ends up takeing that kid under her wing, same way Rainbow Dash took Scootaloo under her wing.