I've played through Adventure Ponies with each of the Mane Six through at least once, and I have learned how each of them play through:
- Twilight Sparkle: Magic laser gives long distance attack options.
- Rainbow Dash: Strong Dash attack, but must be a certain distance away.
- Applejack: Strong kick, but has short range and must face backwards to use.
- Pinkie Pie: Long-range Party Cannon.
- Rarity: Same as Twilight. Should've fired sewing needles instead of magic laser.
- Fluttershy: The Stare is powerful, but has short range.
Of all of them, I find Twilight, Rarity, Pinkie, and Fluttershy the easiest for me to work with. The first three for their long-range attacks, and Fluttershy for having flight and a strong attack. Rainbow Dash is medium because of her flight, but her Dash attack is hard to pull off if you can't get far away. Applejack is the hardest because of how her attacking is done.
What Pony plays easiest for you in Adventure Ponies?