Rarity proving how much she cares for Twilight by telling everypony in Ponyville how she and the others betrayed Twilight, and asking them to write Twilight letters showing her support. This results in Twilight reading through an impressively sized stack of letters filled with gratitude, support, and encouragement from Derpy Hooves, Mayor Mare, Cheerilee, Lotus and Aloe, Mr. and Mrs. Cake, Scootaloo, Sweetie Belle, Snips and Snails, and many, many others, showing just how much love and respect Twilight has earned during her residence in Ponyville. Twilight was actually smiling by the time she got to the final letter from Rarity herself, vowing they will atone for what they did to Twilight even if it takes forever.
Rainbow Dash and Fluttershy going so far as to beat themselves up to get Twilight to admit she still considers them friends.
When the Doctor manages to rescue Dinky Hooves, only to be captured by one of the bad guys who drops the two from Cloudsdale. Cue the tears as Derpy Hooves, who has spent the entire fan fic catatonic since Dinky was captured, becomes the second pegasus to perform a Sonic Rainboom in order to rescue them. The heart beats even faster when Rainbow Dash, seeing this, leads the rebel ponies in cheering Derpy's name and Pinkie Pie's father whispers "Good for you, Miss Hooves".
Let's not forget that Derpy, after performing the Rainboom, ranks that moment as Number Three of her happiest moments? One and Two? Dinky's Birth and meeting the Doctor.
Flim of all people convincing Spitfire to forgive Rainbow Dash in Abundance.
Faith's big brother Honesty coming by and looking after him after Faith's emotional breakdown. Regardless of where this goes, it's good to know that at least one member of Faith's family is still willing to treat him like family.
The Should-Have-Been King
In the flashback to before the founding of Equestria Merida and Tydal discover foals Celestia and Luna and Merida goes on a long speech about how they could teach them to be better and in turn redeem the feuding pony race. She turns to ask Tydal if they could adopt them... only to find Tydal already cuddling them, having decided even before she spoke he was going to raise them as his own.
The fact that the warrior culture that is the capricorn race managed to unite thanks to Tydal and it was because of him and his family's love that Celestia and Luna would later create Equestria.