Phish, LivePhish 16 (Las Vegas 10/31/98)
While I do think some of their studio work is underrated (I'm partial to 1998's Story of the Ghost and 1996's Billy Breathes), I'm reaching into my extensive collection of live recordings for what I consider to be their definitive recording -- not because it's their best show, but simply because it shows off the various aspects of the band I find appealing.
Set one is a pretty standard set, with a few live favorites played fairly concisely ("Mike's Song/Weekapaug Groove," "Punch You In The Eye," "Chalk Dust Torture") mixed in with some material with the then-current Ghost album ("Frankie Says," "Roggae," "Birds Of A Feather").
Set two sees the band donning their Halloween costume -- as has been traditional for some time, each Halloween they become another band and cover a classic album in its entirety (amid other theatrics). In 1998 they went with the Velvet Underground's final album, Loaded, which lends itself particularly well to Phish's loose jams. Now, it's not exactly a note-perfect performance, given that they probably had to learn the whole thing over the course of a weekend. But it's incredibly fun, with the band stretching out in a few places and really giving the songs room to breathe (i.e. a lively "Sweet Jane," a triumphant "Oh, Sweet Nuthin'"); they go all in on "Rock and Roll," which went on to become a mainstay of the band's live repertoire.
Finally, you get the stunning set three, where they take one of their poppiest stand-alone songs, "Wolfman's Brother," and stretch it into a half hour of ambient jamming that would do Brian Eno proud. This is the snippet I like to play on auto-repeat when I'm dealing with insomnia or stuck on a long flight, just me and my headphones and the entire damn cosmos. (And while they could have clearly stopped there and left us woozy, they pull out two more brief journeys, "Piper" and "Ghost.")
Anyway, I'm not looking to convert the unconverted, but if you're on the fence, start here.
Here's the entire third set; skip to around the 7-minute marker to hear the weirdness kick in.
Download it from LivePhish. (The CD version is out of print, but you can maybe find it used on Amazon.) Both versions append a fourth disc with music from the prior night's show, and it's great, probably more illustrative of a typical Phish show from that era.)