Sean... you should bite your tongue (among other things)
Greg was definitely not the bombastic one... and pretentious could be attributed to everyone on the face of the planet.. He is a totally gifted musician and voice, as well as producer.. he's got an ear of gold... and he only gained in talent after he left King Crimson.
His decision to leave KC was the best choice he ever made. As you can see, he and Bob would of ending up killing each other if he had stayed.
Regarding those 3 bands... I, of course selected King Crimson. The voice is the most important thing in KC and ELP to me...
HOwever, I love Keith's piano moments.. so I like "Five Bridges" also. I've only heard a couple of the Atomic Rooster's albums after Carl left.. I wasn't all that fond of them.
However on your list, you left out "The Shame"