Luke, you asked a question, "who ended their career on the best highnote?" - you didn't specify on an individual contest. I answered with my opinion, that is, retiring as the undefeated Heavyweight Champion of the World - I'm sorry if my answer didn't fit your criteria. Fyi - Marciano's last fight was not against Don Cockell, it was against the great Archie Moore, an exciting contest of 5 KDs and plenty of action...a pretty good highnote in itself!
Steve Collins ended on a winner i think but gets accused of ducking Calzaghe. Collins definatly enjoyed the most success towards the end of his career though, beating Eubank twice and feasting on Benns rotting corpse
Every great fighter has one last great fight in them and that's the night they should hang them up in terms of the thread. The reality is they still get good money offers. Jones should have retired after Tarver Mosley after Margarito etc