I don't have any suggestion on this topic because my knowledge on mangoes is really superficial. I think that all the points brought here are valid for your neightbour, expecially the taste sampling.
Anyway, if we speak about fruit trees in general, i would suggest older varieties. Usually for those you find better advice, more knowledge, and strong points and flaws are well known. I can imagine that new varieties have flaws too, they just haven't shown up because the lack of time in cultivation.
I usually prefer older varieties for another reason: often they are centuries old, and hundreds years ago people weren't able to spray plant with chemicals, so usually older (very old) varieties are also stronger aganist pathogens. Centuries ago a susceptible cultivar, even if good flavored, wasn't useful if it wasn't able to bring fruit because of pests. This translates in less chemical around (a good thing), less fuss around to cure the plant (a good thing), some money saved, and more healty fruits.
You in florida apparently live in a strange situation: you have developed some really awesome varieties of mangoes that have become a worldwide standard for this plant. BUT as often pointed, this plant isn't indigenous of florida, this means that probably the better suited cultivar for your climate aren't the older in absolut, but simply the solid old florida varieties. Some new (developed or imported) varieties can also be well suited for your environment (even older cultivar have been "new" at some point in the past), but i think that for casual grower older/well known/widespread cultivar can be a safer bet.
Just my 2 cents.