I'd say right now, it's really a draw. I have a Springfield Milspec Parkerized, and love it. I just love the old military look. The AO was my second choice, almost got one, as the local gunshop didn't have any SA Milspecs, but had an AO, but it turned out it was NOT the WWII Parkerized model, so I passed, and waited, and got my SA at a gunshow.
The AO might have the advantage of being a little less $$, and having all of the parts made in the US. I'm not sure if the cast frame is REALLY that much of a negative.
Two peice barrels in the SA a problem? Never heard of any problems. Maybe not accepted to be as accurate as one peice barrels, but I can't tell a difference. Most people won't be able to.
I think price, and warranty should be the big kickers. I know some time in the future, I want to get an AO to check it out.