Hmm. Well I've done a lot of non-metal. I'd say my favourites included the Mahavishnu, Brand X, MMS albums I did (or anything that was more musically mind-bending). Jazz/fusion/technical stuff are my favourite styles of music. Back in the 70s I was doing A LOT of that sort of stuff. One album I was asked to and was really really hoping to do was the second Cynic album that never happened.
Most of my favourite producers are not metal producers at all. People like Teo Macero, Bob Thiele, Norman Granz, Mutt Lange, David Foster and Todd Rundgren some of my favourites. My favourite metal producer is Colin Richardson without a doubt.
Neil K.