You say you want the national flags that were used most. Used in what context? In early 17th century Europe, 'national' flags were mainly flown on royal warships and fortresses, and often changed from one reign to the next. Are you looking for naval ensigns? Or standards for military units? Those were usually not to any set pattern in this era, but more 'as the colonel may direct'. Or are you looking for some other kind of flag? Trying to help, here.