The answer is simpler than people expect: it depends on why you are watching.
If you are watching an English-language film to relax, use Vietnamese subtitles and enjoy the story. This matters most when your English is still developing. Forcing yourself onto English subtitles means you will not follow the film, the experience suffers, and you do not get the relaxation you sat down for.
If you love a particular film and want to mine it for vocabulary, phrases and pronunciation, set aside a separate session to rewatch it. Pause it. Take notes. Look things up properly and study the language being used. That is the only way this turns into real learning.
Back to watching with English subtitles throughout. If you are at a decent level, meaning you follow roughly eighty percent of what is happening, you will pick up some new words and pronunciations. Below that, the effort neither teaches you much nor leaves you with an enjoyable evening.
Decide what you are there for first, then choose accordingly.