And Rainbow Dash is a ponified Donald Duck! seriously though, there are episodes out there that give Rarity some extra dimensions, Suited for success is perhaps the best remembered, The best night ever had her give Celestia's snobbish distant nephew a particularily brutal reason-you-suck speech, Sweet and Elite was about her inner conflict over whether impressing the Canterlot elite was more impotant than her friends and she was well used in secret of my excess by practically tapping into Spike's memories and reversing the change brought on by greed which by the end of the episode made Spike (ping pongs back and forth between Element of logic and spirit of determination) determined to learn how how to fight his instincts.
You could say that Rainbow Dash also has her flaws emphasized more than her virtues, but once again, since she is basically Donald Duck in the form of blue mare, that is to be expected.
I know he isn't one of the Mane six but Spike is still a very important main character (and my favorite) nonetheless so I'm adding him.
Spike: Owls well that ends well, hands down, really shows that despite being a tactless slacker, Spike often takes his role as Twilight's sidekick very seriously. It also showed his jealous side, which I think he is more prone to than greed, which he's learning to overcome.
Twilight:Look before you sleep is pretty high on my list because listening to her in that episode, made it obvious that she has Aspergers, making it easier for me to relate to her.
Fluttershy: Putting your hoof down
Rarity: Sweet and Elite
Pinkie Pie: Party of one
Applejack: the last roundup
Rainbow Dash: Read it and weep