They sweeten up as they cure. After we pick them before the first frost, they get more time to cure in the sun before we even attempt to eat them, I generally need to wait until November before they are the best.
Generally you wait until you can't puncture the skin with your fingernail. Otherwise they won't be delicious. My mother was picking here too soon 2 years ago and was wondering why they weren't good. They are a winter storage squash, and should be treated like pumpkins.
I find butternut squash extremely tasty, so they are one of my specialty. I grow no other variety or type of squash, except for pumpkin hybrids.
I don't know southern gardening though, so it's possible it's a bit different down there.
See, I like my butternut squash.