As I wrote in another post on this topic, I really can't see why SAS would order anything other than 737s for European work.
I think the question basically comes down to the expected role of these AC. Are they for the European trunk routes only or do they want to use them to supplement the 330/340s on long and medium range routes (eg. over the atlantic, middle east, India).
If its for the European trunk routes (mainly CPH-ARN, CPH-LHR, CPH-FRA, ARN-LHR) then the 739 should be the ideal AC, as these really do not need the extra range of the 757.
If they want to start up services to north Africa or middle East which they don't operate at the moment (apart from Tel Aviv (MD83)), I bet the 736 or 737 would do just fine.
However, the article in the Norwegian newspaper stated specifically that the new AC would be used for overcoming slot shortage at European airport. Hence, my guess would be the 739 or more 738s unless they get a really good deal on A321.