I'd say a Micromussa sp. mainly because of how aggressively it appears to use its' sweeper tentacles. It'd be more unusual for a Favia sp. to do this. Unfortunately, it's generally impossible to tell for certain what a coral is without a skeletal examination, which means killing at least a portion of the animal. Species ID is definitely not possible for most corals without it, and often genus ID is impossible without it too. I find in general Micromussa sp. corallites are smaller than Favia sp. corallites, with Micromussa sp. being in the ~10 mm range.