Do we pronounce ment as MUNT or MENT ?
It's complicated. If you're a learner, I think you should try to imitate the pronunciation of these words directly, rather than by analogy with other words. But if you need to use one of those two options, I'd recommend going with "munt".
The vowel found in the words "money" and "hunt" is usually transcribed as /ʌ/, and the vowel found in the words "penny" and "meant" is usually transcribed as /ɛ/.
The vowel found in the last syllable of "moment" and "environment" is usually transcribed with a third symbol, /ə/.
In English, the symbol /ə/ represents a "reduced" vowel sound: in most accents, it is only found in unstressed syllables. So /ə/ doesn't exactly contrast with the other two vowel sounds. And in fact, the symbol /ə/ does not just represent one vowel sound ("phone"): it represents a range of different pronunciations, some of which overlap with the pronunciations used for other IPA symbols. The pronunciation of /ə/ can be affected by surrounding sounds, and it also can vary between speakers.
Typically, the stressed vowel sound that is thought to be most similar to /ə/ is /ʌ/. But in the context of words ending in /ənt/, some speakers use a quality that certain other speakers tend to hear as /ɛ/. So far, I haven't encountered any speakers who think that their own pronunciation of words like moment or enviroment has /ɛ/ in the last syllable. So I wouldn't recommend using [ɛ] here. I give a longer summary of the sources I've seen that talk about this in my answer to this Linguistics Stack Exchange question: When should I use /ə/ or /ɪ/ and why does it seem like they're not used correctly?
I am an American English speaker, and I think that the way I pronounce /ə/ in words like moment and environment is closest to my /ɪ/, but also similar to /ʊ/ or /ʌ/. I'm not saying you should use my pronunciation: my point is that the vowel in the last syllable of these words can sound like a lot of different vowels, depending on the speaker or listener. Unfortunately, it's not as simple as a two-way choice between munt or ment.