Counter - the fridge will turn it black, but the mold will take longer to grow
I don't know about fridge versus counter, but, I DO know that if you separate the bananas and put them in different places on the counter, (where they are not together) they will not ripen as quickly. I saw this on a TV cooking show and tried it and it works. :) Try it. My roommate does not like that there are bananas scattered here and there...but, it works.