Both looked dominant at LHW before moving up and capturing the biggest crown in boxing. I'd personally take Michael Spinks at both weights. Though Michael Moorer had pop, accuracy and underrated boxing skills, Spinks is mentally the tougher customer in what would be a long, competitive match. Spinks has that awkward movement and rythm going for him, and I don't know if Moorer deals with it well over the long haul.
At light heavyweight, Michael Moorer was only in his early 20's, very inexperienced and probably fighting at a weight that he had to work too hard to stay at. Watching His bout with Lesley Stewart who was far inferior to Spinks, Moorer was outboxed for much of the evening until he was able to capitalize on Stewart's weak chin to win the fight. Jinx was a master at 175 and I don't think Moorer was developed enough to beat him there. At heavyweight however, the positions were reversed. Moorer was better suited physically for that division, had the power to hurt guys, could take a better punch, and ultimately had more fights against top raters. A 1985 heavyweight rendition of Spinks vs a 1994 Heavyweight Moorer might have made for a good scrap.. But I'd favor Moorer over 200 while I'd favor Spinks at 175..
At heavyweight, an aging Larry Holmes in their first meeting might be the only exception, and I would consider that version of Holmes as only being marginally better than some of Moorer's best wins if even at all.. Spinks was gifted a decsion in the rematch.. Tangstad and a shot Cooney don't size up to Moorer's best opponents. And Michael Moorer beat a much deeper and larger array of fighters over 200 lbs.
I don't know wether anyone ever noticed but Spinks has huge fists, nothing relevant to this thread I know.