Obviously dry cargo wise I've seen the "Berge Stahl", larger still was the "Burmah Endeavour" when she was laid up in Southampton (at the time the 8th largest vessel in the world). Largest I've been on board was the "Doceriver" at just under 80,000grt (invited on board by the sparks who I met taking photos at Immingham). Largest sailed on is POR/POH.