I find TLAs [three-letter acronyms] easier to parse, and so I say PHB and DMG, and never MM -- the Monster Manual is always said in full.
I think (though I'm sure there are counter-examples) that two-letter acronyms work best when the last syllable is open (i.e. ends with a vowel sound, as in BC, AD, DC, AC) or labial humming (not as dirty as it sounds -- AM, PM, GM, but strangely not MM, because of the break in the middle: em | em, as opposed to (e.g.) emtee). Its two-letter acronyms that end in F (though I do use the labio-dental CF in speech), H, N, S, and X that somehow feel awkward.
So TLAs for me, so PHB and DMG, YMMV.