In Sweden we have salted and extra salted butter. I always buy extra salted butter. I don´t really know if we even have unsalted butter, if - that must be rather new on the market. I have only seen American recepies using unsalted butter.
When you bake you usually have to add salt - especially when you bake bread.
When using unsalted you have a better control over the amount of salt you use.
I found an interesting (?) explanaition of salted and unsalted butter in Swedish.
To keep butter fresh in the old days it was saltet very much. Before one could use it for cooking and baking one had to wash it. That was done in water. Take a piece of butter and kneap well in a bowl of water, water gets salty and the butter unsaltet. When one was baking sweet things the butter was washed extra well.
Maybe that is why we talk about saltet and unsaltet still today.
Saltet butter keeps longer than unsaltet.
Get the unsalted version. I always buy unsalted butter. I am of the opinion that you can always add salt if you need but you cannot take it out if you don't need it. I also make my own cultured butter (read Irish butter this is what it is) . It is cheaper than the regular butter if you make it home and so fresh and yummy.