Doug Kaye writes, in reference to a list which places REST before SOA;
It also tracks the scales of tight-to-loose coupling and the availability of supporting technologies.
(suggesting that SOA is more loosely coupled than REST)
I don’t have much of a feel about how loosely coupled “Orchestration” is, but I do know that REST based services are more loosely coupled than SOAs. Whether or not you believe that REST can be used for machine-to-machine communications, I think it’s pretty clear that REST uses late binding, while SOAs do not, since REST constrains the interface. Amoungst other things, this means that any agent can exchange data with any service, past, present, or future. You can’t do that with SOA, because you don’t know the interface that future services might use to exchange data.
An interesting question would be, what would a late bound version of an SOA look like? And wouldn’t this be worth pursuing?