To be honest, I'm not a huge fan of the series and never have been, and though I've seen all of the episodes now, most of them are in the like to not too bothered category. I was a comic girl, not an animation girl where MLP was concerned.
So I've gone on nostalgia and only counted the four episodes I had as a child on VHS - which were:
-Ice Cream Wars
-Revolt of P.E
-Sweet Stuff and the Treasure Hunt
-Wouldbe Dragon-Slayer
Of these four my least favourite is the last one. Even though as I type this I can hear that annoying song about being a knight in my head.
Ice Cream Wars amuses the heck out of me but it's not my favourite.
Of the other two, I like both a lot but I hate the fact that Sweetie is called Sweet Stuff throughout and also hated that fact as a kid too. As a kid who was hot on absolute detail I hated that she had the 'wrong' name (I didn't know about US names then).
So the favourite is
Revolt of P.E. I think it's where my love of Paradise came from, but I love pretty much everything about it. The crazy furniture. The illogical way in which things happen (like Baby Cuddles going into one building and coming out in the other), and the weird singing furniture regretting the parting of ponies.
So I'm going with that one.
Of the ones I didn't grow up with, I have fond thoughts for Rescue at Midnight Castle, Tambelon, Somnambula (except the names again ruin it) and the Magic Horseshoes.
I always find it amusing that it's North Star who rings the bell. It's beautiful irony
.