Mario & Applejack - Rivals
Blaze & Spitfire - Flames
Peach & Celestia - Princesses
Amy & Soarin' - Love Interests
Shadow & Pinkie Pie - Time/Reality Warpers
Luigi & Lumna - Eternal Second Fiddle
Daisy & Rarity - Polar Opposites
Miles 'Tails' Prower & Derpy Hooves (Huh...not sure what similarities these two could have)
Yoshi & Fluttershy -(...Kindness perhaps?)
Sliver & Twilight Sparkle - (Tele/Magi) Kinesis
Knuckles & Trixie Lulamoon - Just Can't Catch Up