I actually have reasons for each class — I was very purposeful in putting who where!
Twilight Sparkle (Medic Sparkle) I picked a Medic for Twilight because it was more fitting for her, character and skill-wise. Twilight is a scientific mind, and it has been said of the Medic that the 'healing' nature of his experiments are mere side-effects. His scientific enthusiasm, I felt, made him and Twilight a perfect match-up!
Fluttershy (Flutterpyro) Now, this might seem a stretch, but bare with me; all of the classes have some method of murder. Even the Medic comes with his needle guns and his bonesaws. Only one class, however, has the dillusion (that I am aware of) of doing GOOD. Perhaps in a fit of insanity or drug-enduced hallucination, Fluttershy blows rainbows at her friends (shoots fire at her enemies) and tickles them silly (burns them to death).
Applejack (Sniperjack) Complete with "Apple Juice", I figured the Sniper's hunter history, his patience, and his code of sniping (be efficient, be polite, have a plan to kill everyone you meet) was somehow fitting for Applejack. Plus, a hat!
Derpy (Solderp) What else? A close runner up with Braeburn, I had to pick Derpy because… well… Derpy is fun! Plus, I can picture her saying "Take that, Bablo Babbins!" and "Look out! He's got a book!"
Pinkie Pie (Engie-Pie) Pinkie is random; everyone knows this. Her randomness may not fit the Engineer personality-wise, but his method of setting up sentry nests does. Armed with her Sentry-model Party Cannons and her Party Favor Dispensers (Pinkie-Porter not shown here), Pinkie is ready to throw a little party for all her friends to enjoy when they need a break from blowing each other to pony-bits!
Then, of course, we got the other four, who are in more common match-ups.
Big Mac (Heavy Weapons McIntosh) Fitting for his heavy build, implied physical strength, and giant size. It wouldn't be right to do this without the iconic brony.
Rainbow Dash (Rainbow Scout) Fast, able to jump high, and headstrong. Seriously, who else could I match her up with? Probably Demoman. Then again, I coulda made Applejack the Soldier… 'twould have made sense. Hindsight is 20/20.
Rarity (Rarispy) With a more 'professional' attire, a sabatour way of combat, and a more 'delicate' touch, the Spy remains ideal for Rarity. Plus, she can insult ponies' fashion sense while disguised as them.
Zecora (Demozebra) A nack for mixing is the bread and butter of both the Demoman and Zecora (even if they tend to mess with considerably different chemicals) not to mention Zecora strikes me as having a great deal of physical prowess.
EDIT: A lot of people are actually ARGUING with me about this, pointing out who they think fits better with what class — fun fact, most of them associate others to classes they don't fit. Not sure if it's from an act of favoritism or simply an act of 'I don't like change' because most, if not all, of the complainers are using the popular concept.
Folks, I feel I should point out I INTENTIONALLY IGNORED the popular concepts. Why? Because I like my idea better and view the popular concept as fundamentally flawed. What does Twilight have in common with Sniper (Sniping may use math, but the medi gun likely uses some kind of quantum mechanics which seems like it would be considerably more difficult). What does Fluttershy have in common with Medic? Healing? What about the immoral experiments, the killing tools, and turning her allies into death machines? I disagree — she'd make a better Sniper than Twilight, really. Psycho Pinkie just got old, so I put her somewhere I felt worked just as well.
So yes, so EVERYONE KNOWS, I DO KNOW THE POPULAR CONCEPT. I just don't like it, and tried to use a little more sense in where I put who.
Also. Yes, I left Spike out. Why? Because babies don't belong on the battle field. I don't care how mature they are. Deal with it.
Art (C) MLP:FIM (C) Hasbro/Laura Faust TF2 (C) Valve