Trick question since I believe I already know the answer. But I'd like to hear some other views.
I believe that Economic Theory is like Psychology, it pretends to be a science, when really it is a religion.
People base their opinions on their beliefs. There usually isn't enough facts to go on, anyway.
A basic definition of what I mean:
Integrated Economy would be what the EU is aiming for. Seamless easy access for business to span borders. Favours big business.
Isolated Economy would be North America up to the 80s. Tariffs on most things to encourage local sustainability. Favours small business.
Like you said, it's more of a religious subject than a practical one.
For what it's worth, I think the most pragmatic answer is to have an economy that is mostly isolated by obscene tariffs, and then for each category of tariff to have a half-dozen countries granted low-tariff status. Perhaps two per continent. But the important part is that these be the least-competitive countries in their region. Grant low steel tariffs to whichever countries have the lowest volume of total steel trade.