Not sure how others feel about it but honestly, Part 3's Last Train Home is the best ending.
It's one of the few endings to actually get an emotional reaction from me.
I will say though, I'm going through Part 4 right now (just got into the series, plan on making an LTTP when I finish Part 4 and do it for the whole anime up to that point), and got to say... Outside the latest opening (breakdown), the openings for Part 4 are honestly super disappointing. Since they didn't outsource it for the CGI like they did for Parts 1 ~ 3 it felt far more generic. Like 100000000% times more generic.