I go with D, Season 4. Both season 2 and 4 are great IMO. Season 2 had my favorite season premiere, Luna's first episode, and my favorite song (Smile Smile Smile, though Flim Flam Brothers and This Day Aria were pretty good, too), and Derpy's first episode where she got a line. Season 4, however, had my favorite season finale, an amazing villain (Lord Tirek. Sorry, Discord.), Derpy coming back, lovable characters (Coco Pommel, Cheese Sandwich, etc.), and awesome songs (Glass of Water, The Goof-Off, Apples to the Core).

There are so many things to like about season 4 that I would love to watch some of the episodes again.

I just checked the Hub Network Facebook, and a large majority of them said "All of the above".