I thought about a favorite episode when you mentioned "Four Days Out". There are so many! I enjoyed the Salamonca twins, when they came up from Mexico, while they were sitting on Walter's bed with an axe while he was in the shower, them going after Hank and even the one in the hospital after. I guess for me rather episodes it was certain scenes that moved me, like Walter blowing up Tuco's office. There are so many.