Back to Pinkie Pie in the lead. This is such an optimistic song; and optimistic songs translate to Pinkie Pie Leads.

Applejack - Alto 2 (Lowest part)
*Bass Line
Twilight Sparkle - Alto 1 (Second Lowest Part)
*Percussion
Rainbow Dash - Soprano 2 B (Third Lowest Part)
*Low Chords
Pinkie Pie - Soprano 2 A (Third Highest Part)
*Lead Vocals
Rarity - Soprano 1 B (Second Highest Part)
*Middle Chords
And Fluttershy - Soprano 1 A (Highest Part)
*High Chords and High Melody