I got bored and decided to think about which ponies would be inducted into which Lantern Corp. Anyway, enjoy
Rage (Red) - Pinkie Pie
Why? Red Lanterns are chosen based on a specific kind of rage. Rage that is born of personal loss, such as the death of a loved one. So why Pinkie Pie? Well, in Party of One, she goes crazy because she thinks she's losing her friends. (personal loss) that's why I believe she'd be a Red Lantern
Avarice (Orange) - Scootaloo
The Orange light is centered in a single Orange Power battery. (In comics) The battery is represented as being in and of itself parasitic in nature, mentally suggesting to whomever is holding it to take whatever it wants. In one instance, a blue power ring described Larfleeze, (the keeper of the Orange Power battery) as "empty." Larfleeze seeks to fill the void within him by using the Blue Power of Hope. The reason I chose Scootaloo is because she is A; seeking her cutie mark,
and B; she seeks to be accepted by Rainbow Dash.
This isn't avarice or greed, but rather her seeking to fill emptiness I mentioned before.
Fear (Yellow) - Discord
Why? Yellow Lanterns are chosen based on the individual's ability to strike fear into others. Discord manages to defeat the Elements of Harmony by making them afraid of their greatest virtue. He makes AJ afraid of the truth. He makes Pinkie afraid of being laughed at. He strikes fear into their hearts. Simple and straightforward explanation.
Green (Courage/Willpower) - Applejack
Why? In the episode "Applebucking Season," Applejack single handedly saves Ponyville, managing to stop that stampede. In the same episode, she refuses to give up in her quest to harvest the orchard. Being a Green Lantern isn't about being fearless. It's about being strong enough to fight even when you're afraid. Applejack meets that criteria.
Blue (Hope) - Twilight Sparkle
Why? Because during the Discord arc, Twilight is confident that Discord will be defeated by her and her friends, and only loses hope when the elements fail. But then her hope is reignited, and she brings her friends back from being discorded. And also, the Blue Lanterns are considered to be the most powerful of the corps given that they can drain red and yellow power rings, and super charge green rings. Twilight is powerful too. See where I'm going with this? (Rhetorical question)
Indigo (Compassion) - Blueblood
Why? In the Season One Finale, Blueblood pretty well establishes that he feels next to no emotions, save his own vanity and narcissism. The way he treats Rarity and Applejack (her wares) make him the perfect candidate for an indigo ring. In the comics, indigo rings only attach themselves to those who have no compassion, and prevent the wearer from feeling anything but compassion. It's also the perfect punishment for him.
Violet (Love) - Diamond Tiara
Why? If you know comics, you'll probably agree. The Star Sapphires are grade-A bitches. They are hellbent on making everyone become a Star Sapphire. Kind of like how Diamond Tiara wants everyone to be like her. (with a cutie mark)
If'n ya have any thoughts, feel free to comment, or disagree, or suggest a better candidate for a particular Corp.
Have a good evening y'all