Ralli, our beloved user has made a blog about which of the characters of the show are fits into the main position of the episodes? Who does the episodes mainly focus on? Well, I have a different opinion on some episodes for who's episode are who. Here's the list (special thanks to Ralli for the template). I'm only including the main cast on here though. I don't count side-characters (other than the CMCs).

Characters S Episodes
Twilight Sparkle 1 Friendship is Magic - Part 1, The Ticket Master, Applebuck Season (with AppleJack), Boast Busters, Winter Wrap Up, Feeling Pinkie Keen (with Pinkie Pie), A Bird in the Hoof (with Fluttershy)
2 Lesson Zero, Luna Eclipsed, It's About Time, A Canterlot Wedding - Part 1, A Canterlot Wedding - Part 2
3 The Crystal Empire - Part 1, The Crystal Empire - Part 2 (with Spike), Magic Duel, Magical Mystery Cure
4 Princess Twilight Sparkle - Part 1, Princess Twilight Sparkle - Part 2, Three's A Crowd, Twilight Time (with the Cutie Mark Crusaders), Testing Testing 1, 2, 3 (with Rainbow Dash), Twilight's Kingdom - Part 1, Twilight's Kingdom - Part 2
5 Castle Sweet Castle, Amending Fences (with Spike), What About Discord, The Hooffields and McColts (with Fluttershy)
Applejack 1 Applebuck Season (with Twilight), Look Before You Sleep (with Rarity), Fall Weather Friends (with Rainbow Dash)
2 The Last Roundup, The Super Speedy Cider Squeezy 6000
3 Apple Family Reunion, Spike at Your Service (with Spike)
4 Bats! (with Fluttershy), Pinkie Apple Pie (with Pinkie Pie), Simple Ways (with Rarity), Somepony to Watch Over Me (with Apple Bloom), Leap of Faith
5 Made in Manehattan (with Rarity), Hearthbreakers (with Pinkie), The Mane Attraction
Pinkie Pie 1 Griffon the Brush Off (with Rainbow Dash), Swarm of the Century (with Fluttershy), Feeling Pinkie Keen (with Twilight), Party of One
2 Baby Cakes, A Friend in Deed, MMMystery on the Friendship Express
3 Too Many Pinkie Pies
4 Pinkie Apple Pie (with AppleJack), Pinkie Pride, Maud Pie
5 The Lost Treasure of Griffonstone (with Rainbow Dash), Party Pooped, The One Where Pinkie Pie Knows, Hearthbreakers (with AppleJack)
Fluttershy 1 Dragonshy, Swarm of the Century (with Pinkie Pie), Stare Master (with the Cutie Mark Crusaders), Green Isn't Your Color (with Rarity), A Bird in the Hoof (with Twilight)
2 Putting Your Hoof Down, Hurricane Fluttershy
3 Keep Calm and Flutter On
4 Bats! (with AppleJack), Filli Vanilli, It Ain't Easy Being Breezies
5 Make New Friends but Keep Discord, Scare Master, The Hooffields and McColts (with Twilight)
Rarity 1 Look Before You Sleep (with AppleJack), Suited for Success, Sonic Rainboom (with Rainbow Dash), A Dog and Pony Show (with Spike), Green Isn't Your Color (with Fluttershy)
2 Sisterhooves Social (with Sweetie Belle), Sweet and Elite
4 Rarity Takes Manehattan, Simple Ways (with AppleJack), Inspiration Manifestation (with Spike)
5 Canterlot Boutique, Rarity Investigates! (with Rainbow Dash), Made in Manehattan (with AppleJack)
Rainbow Dash 1 Griffon the Brush Off (with Pinkie Pie), Fall Weather Friends (with AppleJack), Sonic Rainboom (with Rarity)
2 May the Best Pet Win!, The Mysterious Mare Do Well, Read It and Weep
3 Sleepless in Ponyville (with Scootaloo), Wonderbolts Academy
4 Daring Don't, Rainbow Falls, Testing Testing 1, 2, 3 (with Twilight)
5 Tanks for the Memories, The Lost Treasure of Griffonstone (with Pinkie Pie), Rarity Investigates! (with Rarity)
Mane Six 1 Friendship is Magic - Part 2, Bridle Gossip (with Apple Bloom), Over a Barrel, The Cutie Mark Chronicles (with the Cutie Mark Crusaders), The Best Night Ever
2 The Return of Harmony - Part 1, The Return of Harmony - Part 2, Hearth's Warming Eve
3 Games Ponies Play
4 Castle Mane-ia, Power Ponies (with Spike), Trade Ya!
5 The Cutie Map - Part 1, The Cutie Map - Part 2, Do Princesses Dream of Magic Sheep?
Spike 1 A Dog and Pony Show (with Rarity), Owl's Well That Ends Well
2 Secret of My Excess, Dragon Quest
3 The Crystal Empire - Part 2 (with Twilight), Spike at Your Service (with AppleJack), Just for Sidekicks
4 Power Ponies (with the Mane Six), Inspiration Manifestation (with Rarity), Equestria Games
5 Princess Spike, Amending Fences (with Twilight)
Apple Bloom 1 Bridle Gossip (with the Mane Six), Call of the Cutie
2 The Cutie Pox, Family Appreciation Day
4 Somepony to Watch Over Me (with AppleJack)
5 Bloom and Gloom, Brotherhooves Social
Sweetie Belle 2 Sisterhooves Social (with Rarity)
4 For Whom the Sweetie Belle Toils
Scootaloo 3 Sleepless in Ponyville (with Rainbow Dash)
4 Flight to the Finish
Cutie Mark Crusaders 1 Stare Master (with Fluttershy), The Show Stoppers, The Cutie Mark Chronicles (with the Mane Six)
2 Hearts and Hooves Day, Ponyville Confidential
3 One Bad Apple
4 Twilight Time (with Twilight)
5 Appleoosa's Most Wanted, Crusaders of the Lost Mark

Episodes will be added as season 5 progresses.

Any opinions?