statistically, as most marriages are between a jew and a non-Jew, the one with the Jewish last name is Goyish (Jewish father), and the one with a non-Jewish last name is Jewish.
Seriously, distribution is uneven. There are whole pockets of Jews where most are non-Jews (Reform temples in the south?) and pockets where there is rov yehudim: Israelis, Brooklynites, Russians from smaller towns in Ukraine. Uzbekistan, etc …