Hi Arcticfox,
I'm afraid, but my answer is likely to make this an offtopic thread - I don't see any Oneworld programs as the best, as you are very likely to need a lot of connection flights if you travel from ZRH/STR to almost anywhere except LON/MAD/HEL/AMM/BUD/JFK. Also otherwise OW programs have some shortcomings:

-BA: no status accrual on discounted economy, no accrual at all on AA transatlantic flights.
-AY/IB: better than BA on discounted economy and AA transatlantic, but featuring another low tier ("ruby") before you achieve higher tiers.
-MA: also decent on discounted economy and AA TATL, but top tier ("emerald") by invitation only!

It's likely that *A will be the better solution for you. There are LH/LX, SK and BD the main options. Most posters in FT prefer BD, due to relatively low requirements for Gold. I'm personally on LH/LX as I think there is always an advantage of using a FFP from your home country. This offers better availability of reward bookings, additional promotions etc. On all three programs you can collect (a few) miles even on discounted economy. There is a vast selections of flights out of ZRH/STR using LH/LX and to Scandinavia even SK.

I hope this helps,
Swiss_Global