My top three would be:
3- Party of one: A classic episode with Pinkie Pie at her best and lots of moments for the posterity.
2- For whom the sweetie belle toils: I don´t know why but I love these episode although I usually don´t enjoy the obligatory Christmas Carol episode in all the series. I specially love when Sweetie discover what her sister did for her at her birthday, all the scene is so cute.
1- Twilight's Kingdom: This episode have really all the ingredients to be one of the bests episodes in all the show; Action, fun, an strong villian, Discord, A great ending...
I would also like to include Pinkie pride, It's about time, make new friends but keep discord, testing testing 1,2,3, over a barrel and more.