Keitt would be my favorite as an all around late season pick. The flavor is good (not quite excellent), but finding an excellent tasting mango that consistently produces late season is a challenge. Production is consistent and heavy. In Florida, crops can last until October in some years, but September crops are a sure bet.
Keitt can be extremely disease resistant, and it can also be very disease prone. I've seen both. But in a dooryard scenario, it tends more towards being disease resistant. I have had problems with MBBS, but a hard pruning seams to have solved the issue.
One thing to keep in mind when selecting a late season mango is that you can't be overly choosy. You are already selecting based upon a genetic rarity (a mango that produces late). Combining that with the other desirable but rare characteristics (eg, high production, good disease resistance, excellent flavor, etc) means even longer odds that you'll find a winner in the genetic lottery. So, typically we compromise a bit on flavor, which is why most late season mangoes are "good" (vs excellent).