I beleive there are two possibilities
According to the DRAE
felicitación
1. f. Acción y efecto de felicitar.
2. f. Tarjeta postal, telegrama, etc., con que se felicita.
and:
enhorabuena
Tb. en hora buena en aceps. 2-4.
1. f. felicitación (‖ acción de felicitar). Les dimos la enhorabuena por la victoria.
2. adv. Con bien o con felicidad.
3. adv. U. para denotar aprobación o conformidad ante lo que se enuncia.
4. interj. U. para felicitar a alguien.
de enhorabuena
1. loc. adv. En situación afortunada o feliz. Estamos de enhorabuena porque ha nacido el primer nieto.
The motivation for my question is seeing a couple standing outside Málaga town hall who appeared to have just got married. Should I have called out ¡felicitaciones! or ¡enhorabuena! or would that have been inappropriate? In fact as it turned out as we walked along it became clear that they were part of a photo shoot so neither would have been a good idea. It looks from the definitions that enhorabuena would be better. Is that correct?