I've always known guanabanas to be sweet and somewhat acidic, but you ask a very good question.
Because guanabanas seem to be propagated by seedlings, then almost certainly some strains will produce fruit that is more sweet and less acidic than others, and perhaps even more cold resistant.
It's then imperative to propagate, by grafting method(s), these superior strains, in order to keep improving the quality of the guanabana fruit.