I think Web services are best for SOA. If you need to support Distributed OOA, then
you should probably use
Java RMI or IIOP or something with better preformance. That said, I see the days of Distributed OOA in decline to some degree. Most people don't use
EJB, for example, outside of the server (
Servlet - to - EJB). Martin Fowler's first rule of dstirbuted objects is "Don't distribute your objects." I"m not sure I would go that far, but its food for thought.
However, you really can't compare SOA to OOA, becuase they are very compatable technologies. SOA exposes a service and OOA is used to implement the service. At least that's how I see it. They are two parts of the same puzzel.