Welcome, sambalgado. After being based in Ireland for several years, SNN is about to die a slow and horrible death except for European routes. Personally, I would go with ST and *A - specifically Air France Flying Blue for ST and BD Diamond Club for *A.....they are relatively easy to get status for lounge access but are not as generous in bonus mileage and status points as the US based members of ST and *A. So it is a bit of a toss up. I stopped using my UA card only 6 months ago and easily got *A Gold with BD on my LHR flights. Even get free drink and snack when I show the card on BD flights.... Had to work to keep that status on UA, but got more in bonus miles....but no freebies in coach....ever.....

I would think that lounge access is important and none of the European programs are that good, but those two are the best. In relation to OW, the only way to go is AA. Would not bother with BA program, as it is getting worse by the day unless you are paying for J.

Hope this helps.