Since the Hi-Power has been in production since 1935 and it's been used by several 1st world nations as a sidearm, I would say it has this distinction. During WWII Germany (640b) used the Hi-Power as did Canada and England.
To this day the Hi-Power is still in service with the Belgian Army, British Army, Indian Army, Australian Defence Force, Argentine Army, Irish Army, Luxembourgish Army, Israeli police, Singapore Special Operations Force and Venezuelan Army, among others. This doesn't count the Police agencies world wide that still issue the pistol.
The CZ is in use by Czech Army, Chilean Army, Iranian Army, the Sudanese Army. It's also in use by a handful of police departments mostly in 3rd world nations.
Given the P35 has been manufactured for 40 more years than the CZ and through one World War, I would say the CZ has a lot of catching up to do to be labeled the most prevalent.