We're in the same boat, Kempis, except that my SR/LX flights went to my AA account. Because of my lack of SR/LX flights, my QG message says I have been allocated to SN (!)
We won't have the M&M option and will have to choose between LX, TP and SN.
Of these, I prefer LX, because I know I can redeem my miles with AA as well as use them to/from Zurich. In your case, you may want o contemplate LX's wider network?
(Remember when SK and SR were partners? - before frequent flyer programmes.)