I've heard a some cuts from Kiko's solo stuff, it really dig it. I know it's a somewhat subjective metric, but he has great "feel" to go with the technical ability. He also seems like a chill mofo in his interviews. As a musician who has spent many hours in bands with assholes, that means a lot to me.
Mustaine has for sure never fielded anything other than a stellar lineup. As far as drummer/guitarist pairings, I'd rank Menza/Friedman at the top and DeGrasso/Pitrelli at the bottom, personal preference of course.