Which hurricane/tropical cyclone was the strongest?

It may have been tropical cyclone Olivia, April 3-12, 1996, at Barrow Island, Australia, which had peak wind speeds of 408 km/h (253 mph) as reported by the World Meteorological Organization. The storm's central pressures were around 925 millibars, some of the lowest pressures for such a major hurricane. 10 injuries were reported, along with about $2 million damage in US dollars. Super typhoon Haiyan of November 6-9, 2013 may also rank as one of the strongest typhoons ever. According to the US Navy's Joint Typhoon warning center, the central pressure was about 930 mb, with sustained winds of 195 mph and gusts to 235 mph. As of November 9, the storm is estimated to have killed at least 140 persons in the area of Tacloban, on Leyte Island in the Philippines.

Sources: NOAA, Wikipedia, the JTWC, and the WMO