— Antiochian churches have an Arab heritage. Greek churches have a Greek heritage. Antiochian and Greek come from the Byzantine liturgical tradition. OCA churches have a Russian heritage and Slavic liturgical tradition.
— Antiochian and OCA will be completely or mostly English, while the Greeks tend to use both Greek and English more equally.
— Most of our worship is done standing. OCA is less likely to have pews, while Antiochian and Greek parishes tend to have them. (Pews or not, every church I've been to has had seating available for people who cannot stand, incase that's a problem.)
Beyond this and apart from liturgical minutae, it's hard to say what they will be like. Every parish will have its own flavor. I would visit all of them and see where you feel more at home.
As far as ethnic issues, that also depends on the individual parish. I go to an ethnic parish and I never felt like I was being rebuffed. I've never met anyone who has told me they have been. The most I've heard was confusion ("Why would an American want to be Orthodox?"), but not hostility. I'm sure those kinds of parishes exist somewhere, but their presence is a bit overblown I think.
I hope your visits go well!