Thunderstrike. Only way Omega could win is with deathspores. He isn't outranging thunderstrike and he isn't going to physically overpower someone able to go toe to toe with Thor.
i'm not sure why the spores would fail on TS but, i doubt it.
@Uriel
OR is pretty strong and can increase his strength while at the same time weakening his opponent putting them on equal ground if not putting OR in a superior advantage