No disrespect to Spinks but being a 35 year old who became a serious fan at an early age in the early 80's, I have to go with Michael Moorer as my #1.
Spinks #2, but Double M #1.
Moorer was a murderer at LH. 22-0 (22 KO's) as a Light Heavyweight. I remember seeing him for the first time on an ESPN show in the late 80's and watching the opponent become intimidated the moment Moorer stepped into the ring.
It's not like he was a failure as a heavyweight either. I know history has not been kind to him, a lot of that he can blame himself for, but nobody can take the masterful performance over Evander away from him.