Thank you for your answers,

EuroBonus Gold would indeed be the best option, however, I’m not sure I’ll fly enough on SAS (or collect enough miles on other carriers) to achieve it. From what I can tell so far, SWISS and Lufthansa will remain my primary carriers, so I wouldn’t want to leave M&M FTL just so I can maybe get EB G. Miles&More would therefore (at least for now) remain my main programme and EuroBonus would just be, well, a bonus : )

And I see you were right about the lounge access — I seemed to remember it was part of the deal for EB S, but I just double checked the website and I indeed noticed the fine print below (Valid July 1-August 31 and December 15-January 15?!).

Regarding the crediting of flights, what I had in mind, was this; lets say I have a ticket from Stockholm to Luxembourg: ARN-FRA (on SAS), FRA-LUX (on LH), LUX-ZRH (on LX) and ZRH-ARN (on SAS).

The idea is that I retroactively credit the ARN-FRA and ZRH-ARN flights to my EuroBonus account and the FRA-LUX and LUX-ZRH to Miles&More. Would that be possible/allowed, or would it not make any difference, since all four flights are on the same ticket?