1) Favorite MLP episode(s)? Favorite episode ever: Best Night Ever - This episode is just all-around fantastic. Some of the best song-writing of the season (And I hate broadway-style singing in anything, so you know if I liked it, it was good), great comedy, and the Mane 6 ALL get some excellent character development. Best way to end a season.
Other favorites:
Lesson Zero - This one is just too funny, especially when Twilight has her "breakdown". A classic.
The Return of Harmony - Come on, do I really need to explain this one? The writing in this one alone puts most other cartoons to shame.
Dragon Quest - Top notch writing, and it reveals more depth to my favorite non-pony character on the show. Suited Fore Success - Everyone berates Rarity for being greedy, but this episode clearly shows her being generous. Green Isn't Your Color - The moral to this one is just fantastic.
Too Many Pinkie Pies - This one features my favorite of the Mane 6 with some of her best comedy writing.
Bridle Gossip - How can you NOT like this one? Pinkie Pie is in top form, and you get to know Zecora; a character they use mostly as a plot device, and more than deserves to have her own episode. Not to mention the poison joke, I laughed so hard at Flutterguy.
2) How often do you go back to watch the show? Occasionally, when the mood strikes.
3) Do you do it in groups of episodes, a single, or marathon an entire season in one go? When I first became a brony, I watched every episode in chronological order all the way through, but I'll go back and watch one episode here or there. Usually when I remember something from an episode, and just want the nostalgia. Or checking on an animation error.
...and if you choose,
4) Favorite season? Season 1, it contains the most of my favorite episodes. In season 2, it just seemed like they were experimenting with the writing (Too many Rarity-focused episodes for me). In season 3 the writing and comedy were top notch, but just not enough good episodes (It was just a victim of poor timing).