I would have REAL trouble deciding.
I guess Tull, Pink Floyd and Yes are right up there.
tull is just REALLY COOL
pink floyd is just "right". they kick ass. they might not be the most skilled or fastest musicians, but they sure as hell know what they are doing. The wall, Dark side of the moon and wish you were here are just TOO HARD to beat.
And yes... Close to the edge is currently stapled to my turntable.

basically i like all things prog, but those are just the greatest for me. Not even porcupine tree measures up (who has btw just overtaken Spock's beard in my preference list).

So what do you people think? care to share?