Friendship is Magic part 1 and 2. Honestly, I've never seen a better introduction to a group of characters with very different personalities, likes/dislikes, of course design and actually like all 6 throughout the first and second seasons. Though the monologue Twilight gives on part two about being friends with the other 5 is pretty...*gags*...and sometimes I think about skipping it, I just find these two episodes atmospheric since its introducing the world of Equestria for the first time.
Not sure what my obsession with atmosphere is, but...yeah....just love it...