My parish is Greek.
As others have said, the Church is one. The differences are in some visual style, music composition, languages used, ethnic traditions, and sometimes vary between parishes in the same jurisdiction in some things.
I have found OCA and Antiochian to be very similar in some of the ones I have visited. The only differences in the ones I visited are that the OCA was sometimes slightly more Slavic-leaning (and that was probably the particular parishes I have visited and the people that happened to make them up - one OCA parish I visited was very much NOT ethnic). And that in OCA there were more headcoverings to varying degrees, and often no pews.