While I do not know the ins and outs of everything in Sweden, and so will leave that to others, I would say that in terms of usefulness in Europe (and Asia for that matter), AMEX is the most useless credit card in the market (mainly due to their fees causing retailers not to accept).

If I were you, I would get the MC and have the AMEX as a secondary card if you see any benefits in it - personally, I have a corporate card from AMEX which is a pain to use in most places.