Which varieties to grow? The real issue with summer squash is that the aphids like it. Whats more they spit digestive juices into the plant before they such out what they want. This 'activity' passes on plant viruses that it picked up from another plant. Before too long all your squash plants have the virus and the production fall rapidly. Not a happy situation.
Trying to keep the aphid away is not a battle we can wage as organic farmers. If you grow at high altitudes where aphids do not like to live has its problems like frost and a very short growing season. So the best way to deal with this rather unsavory habit of the aphid is to find varieties of squash that carry resistance to the viruses. This is the main criteria in choosing which ones to grow. There are some round varieties that have no resistance and I grow them because, well they just look good even though they only produce a crop for a couple of weeks.