Amazingly no takers. While having my own ideas here, I was looking was some concensus from the experts.
So let's cover Machine first. Unsurprisingly the covers of their tunes are by friends of the band - and often with one or two players from Machine present. With the large number of Soft Machine live albums out now, there are many band own versions of their compositions. But I believe from that and other artist's cover Dedicated To You But You Weren't Listening wins - e.g. Caveman Hughscore, Keith Tippett Group (who used the song title for the album title).
Now Crimson. Red is probably the favourite - Niacin, Glueleg, Wood, Either Orchestra immediately come to mind. However, Court and 21st Century Schizoid Man may sneak in: (a bit of a cheat to include) 21st Century Schizoid Band, Greg Lake/Gary Moore Band, Steve Hackett. Then question comes up - what have I missed?
Oddest cover?? Zappa doing Yes?