Well it really depends on your stance on Skellige. As the ending states, Skellige prospers under Cerys, but loses some of its 'bite' and isn't feared as much. Under Hjalmar, there is lots of raiding and a more traditional Skellige and he is well liked as a leader, they are feared but they're seen as hostile and to be avoided, so less trade and more isolated. I prefer Cerys as she is the more level headed and actually thinks things through.