These are the groups that I go mad for in the late 60`s to early 80`s period and in no set order:
The Doors, Jimi Hendrix Experience, Supertramp, Yes, Wishbone Ash, Black Sabbath, Fleetwood Mac, Cheap Trick, Aerosmith, Free, Blue Oyster Cult, The James Gang, Led Zeppelin, Deep Purple, Neil Young & Crazy Horse, Talking Heads, Kansas, Styx, Toto, Journey, The Tubes, Alice Cooper, The Who, The Cars, Little Feat, The Band, Love, King Crimson, Jefferson Airplane, Boston, David Bowie, Peter Gabriel, Kate Bush, Mountain, Humble Pie, Grateful Dead, Rush, Sparks, Devo, Squeeze, Stranglers, Survivor and Scorpions to name just a few
As for picking a best 2 out of this diverse bunch..........Well almost mission impossible.
But I`m sure you could pick two?