Looking for some friendly advice....

I fly from the UK to South America every one to two years with my wife and two kids.
We also fly about twice a year within europe.
Since the demise of Varig our long haul flights seem to often be with american airlines. I feel its a waste that I have never collected airmiles for /from all these long flights... but which oneworld program would be best for me. I thought AA at first but worried that the miles expire after 18mths so if I only take a long haul return flight(with 4 people) every 2 yrs the miles might go to waste...

Any advice gratefully appreciated.

Joey.