military-wise, everybody is pretty much on the same page. location-wise, it is a no-brainer. just pick whichever ones are far away from anybody.
for example, England, Scotland, Danemark and Moors have relatively good starting locations. Russia is fairly remote too, but the distances between its cities are annoying as hell.
btw, Sicily also has a very good location, they are also conveniently located next-door to Papal States

. but you will need to rely more on shipbuilding if you want to get around.
the most suicidal starting locations are Turks, Venetians and Holy Roman Empire. you are getting invaded from all directions real fast. Turks get it especially hard, since they are usually owned by Byzantines and countless crusades, and then by Mongols and Timurids.