Fluttershy definitely wins for most relaxing pony. If i needed a camping trip to get away from it all, I'd totally bring her. Otherwise Twilight gets my vote!
And if you are too relaxed over that, have a bit of Twistrike remixing and Smile Smile Smile. Check them out below!
1.) [MLP music] Patrick Poe - Lullaby Fluttershy
2.) ArtAttack - Twistrike (Sonic Breakbeat Remix)
3.) Meelz - Smile (Punk Rock Cover)