I guess it will be hard to keep this one spoiler free, but hopefully people that come in here will read this and know to run away if they don't want spoiled!
You've been warned!
I think I might need some time to think on this one. I have watched the entire series once, and a few eps twice, but I feel I should try them again, with Serenity at the top, to see if my opinion changes any. Right now I tend to agree with your glowing recommendation of Out of Gas, but Ariel was also excellent, and I am still fond of Serenity, even if it did lose something in being aired last.
will update you when I make a decision.
Shall I add a poll?