Check for sweeper tentacles, especially @ night/in dark. If sweeper present, probably a favid, leaning toward Platygyra since valley is not as deep/wide in the pic as Ive seen/handled Oulophyllia.
If no sweppers at all, cant be sure as all the Merulina's Ive seen/handled did not have such thick outer edges, if memory serves although hard to judge from the pic.
In any case, nice piece for sure!