What is the epic song of a group?

Since we appear to be deviating from the criterion of "groups" that was stated in the OP, I’ll add the following to my previous response:

"Both Sides Now" -- Judy Collins (written by Joni Mitchell, of course)
(The original version, that was included in Judy's 1967 "Wildflowers" album and was released as a single in 1968, not the disappointing later version that is sometimes heard).

A masterpiece, IMO.

Regards,
-- Al

Al, speaking for myself, that’s because very few groups have a member capable of writing what I consider a song, let alone an epic one ;-). By the way, though I don't care for Joni (to put it mildly), I agree with you about Judy’s version of "Both Sides Now" ---Eric.

Roll Over Beethoven - Chuck Berry

War - All Day Music
Johnny Guitar Watson - A Real Mother For You
Bruce Hornsby - The Way It Is
Elton John - Levon
Randy Crawford - Knockin' On Heaven's Door
Stanley Clarke - East River Drive
Brad Mehldau - Since I Fell For You
The Crusaders - Hard Times

Gene Clark - Strength of Strings
Pink Floyd - Echoes
Neil Young - Cortez the Killer