Best ST membership for UK resident
 

I do the occasional flight to the US but mostly around the continent. What is the best airline FF to join? Air France, Delta or NWA.

For further info I've flown all three recently.

In that case, I'd say one where you can claim the miles retroactively if you weren't a member of any ST FFP when you flew.

What types of fares (full or discounted) and class of service also comes into the equation.

AF's programme isn't too bad if you are not flying cheap fares (don't earn full miles on that and KL in addition to V fares in NW) as you get ST E+ at 40k miles with a U.K. address. Elite bonus miles aren't so good but you get min. of 750 miles for intra-Europe non-domestic flights (providing the fare earns 100% miles). You also get UGs on NW within the U.S.

If you fly BC, CO may be good as it gives (or used to give) 100% EQM bonus for BC (KL FD used to do that).