Although ashkenazim pronounce a “vav” as an english V, I believe everyone agrees that a W sound is more authentic. That having been said, a long O is almost definitely more authentic than “oy.” The cholam is a vav, and the long O sound ends with a “w” whereas “oy” ends with a “y”
That having been said, I personally asked Rav Moshe Shternbuch what someone who grew up saying “Oh” and now lives in a community where “oy” is accepted should do, and he answered that you should pronounce it how you learned it. I presume the same would apply if you grew up saying “oy.”