The best-tasting watermelon is soaked on the vine, absorbing all the nutrients and sweet flavor. The stem should be yellow-brown, and at the bottom of the watermelon large bright spot should be creamy yellow. I recommend knocking on the watermelon to hear a deep hollow sound, if the sound isn’t hollow it means the brine is too thick. Also if watermelon on the outside has deep, rough weathered spots, it means it's super sweet. Rounded watermelons tend to be sweeter than oval-shaped ones. Lift up the watermelon, it should feel heavier than it looks.