How many miles?
If you link on over to http://webflyer.com/travel/milemarker/
you'll find their MileMarker which is good for multiple legs of travel and determining miles earned.

Which airline program the best? I think the answer depends on which class of service you will be flying. If you don't mind offering that up I think there's a number of people here that can offer up opinions. If in coach, BA likely won't win many suggestions.

Lots of miles to be earned and you are right about trying to pick the right program.

I'll flip this over to MilesBuzz! for opinion since the advice to come will now be related solely to "best" frequent flyer programs for your needs.