Looks like i am on my own here but i always thought Archie Moore (at his best) looked beautifully relaxed in there.
My vote is for Alexis Arguello. The man just flowed. As far as new guys, Mikey Garcia fits the bill. He is always calm, doesn't waste punchers or energy. Excellent timing.
Guillermo Rigondeaux, Mario Kindelan, Mike McCallum, James Toney, Sumbu Kalambay, Donald Curry, Salvador Sanchez, Pernell Whitaker, Wilfred Benitez, Floyd Mayweather, Nicolino Locche, Erik Morales, Samart, Roy Jones, Roman Gonzales, Bernard Hopkins, Ricardo Lopez, Andre Ward.
Yeah, Archie Moore definitely looked relaxed. He was always under control no matter what, even in first Durelle battle.