Here it talks about pony personality disorders and classifies each one (except for Applejack, who’s apparently the sanest of them all).
I identify the most with Twilight Sparkle, with her bookishness, skepticism, and insular lifestyle. She’s pretty damn practical and level-headed for someone who started out so socially awkward, and I’m glad she’s making progress on becoming more well-rounded.
Rainbow Dash is probably my favorite pony, because she has the kind of personality I wish I had. Energetic, driven (sometimes too bloody much), and the ability to achieve awesome things (like the sonic rainboom).
I love Applejack as well, though she works too dang hard sometimes.
The other three ponies get on my nerves much more often. Rarity is such a whiny, high-maintenance priss, who wants nothing more than the latest fashion and Prince Charming. Ugh.
Fluttershy is too soft-spoken and spineless for me to like her. She’s that one person in a group who might get hurt feelings if everypony doesn’t walk on eggshells or says mean things. To be honest, she reminds me of myself when I was younger (painfully shy, oversensitive) and so find her annoying. Geez, I’m sure projecting on these ponies a lot.
And Pinkie Pie is just a damn fool moron who takes nothing seriously. Can she develop the slightest bit of maturity and adult behavior, or is she going to stay a spiritual five-year-old forever?
These are just my personal opinions on the ponies, no offense intended.
One thing I really like about the show is their willingness to take on potentially heavy topics like slavery, intellectual skepticism, and the search for identity (although I am sick to death of the Cutie Mark Crusaders).