Bon appetit is best if you want to say something.
Note that in English speaking countries we don't generally express this sentiment at all.
When we do feel like saying something, among native English speakers I feel the anglicised version of the French phrase is the most common way.
I don't believe I've ever heard "enjoy your meal" used among groups consisting only of native English speakers. It is widely used by people learning English and even people teaching English to foreigners. I think it must be in lots of bilingual phrasebooks, dictionaries, and teaching materials.
Everybody who uses "bon appetit" in English perceives it as French but unless they've studied French or spent some time in a French speaking country, it is mostly mispronounced in that we pronounce the final "t" where French speakers do not. (This is ignoring the many other more subtle differences between English and French pronunciation.)
To sum up:
- If you really want to act like a native speaker don't say anything.
- If you still really want to say something and still be like a native say "bon appetit" but pronounce it bon-app-a-teet.
- If you're worried about "correct English" say nothing or stick with "enjoy your meal".