Tough call, but I'd have to go with "Decade" and "Unplugged". Naturally, I'm willing to cheat here in order to get it all.
"Harvest Moon" is flawless as well, in my book. Oh, and "Ragged Glory" reminds me of the feeling you get when you first join a band, that if you could spend all of your days jamming with your friends, life is good. Amazing album, that one.
Sorry, can't tag just one. I think I might even buy the entire collection if a polyester-wearing gent with a toupee knocks on my screen door to sign me up for a one-per-month club.