The first episode and Misty's departure episode. I cried during both and neither have been topped imo.
My most emotional episode was when Paul left. I never felt anything for the earlier stuff.
Interesting.
The fact you're a big fan of Ash made me definite you'd find him crying in Snow Way Out emotional.
-Snow Way Out.
-Bye Bye Butterfree.
-Pikachu's Goodbye.
I would say the most emotional episode for me is, "Memories are Made of Bliss!" because that was the last Diamond and Pearl episode.