I'm guessing the sweetest is guaquiea (even though i've never tasted), I do not believe the tree will get much taller than 20-25ft? maybe I'm wrong? I believe it's reported to be less than 20ft tall, but I never believe what I'm told...they all seem to get taller than what the books say.
trunciflora is a superb fruit, but a tall tree, and sensitive to high winds, drought....it also takes many many years to fruit (at least the variety I have in FL, takes 15-20yrs approx)..fruits are large, very sweet with a unique flavor (aftertaste reminiscent of a coffee berry, hence the name, Jaboticaba cafe), pulp is very smooth, fiber free, and has small seeds, but numerous 2-5 per fruit approx....skin is thin, with low tannin.
coronata var restinga, supposedly one of the most precocious varieties of M. coronata, taking only about 5-8 yr to fruit from seed, instead of the usual 15-20yrs. Sources in Brazil also say its tolerant of coastal plantings (somewhat cold sensitive, not enjoying temps below 27F it seems)...large fruited, supposedly sweet and delicious. Not sure of tannin content, but I've read the skin is considered thin.
M phitrantha, supposedly one of the best tasting species in the world...but I have noticed this is one of the most fickle species to grow...(seedling trees often languish, I'm assuming due to improper soil biology, or pH that is too high). Grafted trees are much easier to grow, but still can require chelated Fe drenches and micro nutritional sprays...Thank goodness they can be grafted, it makes growing them so much easier (at least for me it did). Keep in mind (as i'm sure you know) there are so many varieties of phitrantha it's hard for me to keep up...if possible, don't plant seeds, get scions from a tree that is a named variety!
(oblongata and grandiflora don't get me as excited as the others, but this could be due to ignorance...I have never tasted them...although I have seen pictures and read reports, and did not find them to be provocative.)