I'm seriously happy that there's a Bananas board because when I go to the supermarket here in Japan, I always wonder what the differences are in the 5-8 varieties of bananas in the produce/fruit section. There's always the regular "cheapie" bananas that cost around 98-128 yen (roughly $1.00-1.40) for a bunch of 4-5 (typically the Dole, Chiquita, Del Monte brand from the Philippines); then there are the varieties that go up from there, up to 400-500 yen for a bunch, usually packed a little more carefully. I've found the good middle-brow brand called Sumifuru that I can find on sale for 100 yen, but usually cost up to 200 yen for a bunch. The main difference I've found between these Sumifuru and the "cheapies" are that they keep their firmness and flavor well past the spotty brown mature stage. The cheapies become pasty and fall apart easily when past their primes.
I've experimented with the more "premium" bananas from Dole or Chiquita, but they just seem to be the same bananas as their cheapies, except maybe they are the "select" bunches handled with a little more care for the picky Japanese market. They still tasted better than their cheapie counterparts though.
Then there are the bananas that are packed for convenience stores (7-11, Family Mart, Lawsons), that are most likely some of the same brands as I've already mentioned, just packaged for these shops. But they seem to be in better shape then those in the supermarkets. I usually buy them at convenience stores only when I'm on my way to a sports event where I know I'll need the potassium during my downtime. But they still seem to taste better than the cheapie bananas that I now tend to avoid.