Winter Squash, as partially defined here, is very easy to determine how good it is or not. Keep your eye open for the following:

• The Squash should be very firm over the complete surface area of the fruit.
• Pick a squash with a stem attached as opposed to one with the stem missing. Also, the thicker the stem the better.
• A matted color is preferable to a shiny color. This include pumpkins.
• Choose one that has a smooth, dry rind and is free of cracks or soft spots.
• Avoid squashes with soft spots or bruises.
• Squashes with thich skins can be stored in cool, dry place for 3-4 months on average.
• Before using, wash any winter squash in cool water.
• Thin skin? Remove the skin. Thick skin? Keep the skin on.
• Squash grown in colder climates tend to have more flavor than those in warmer climates.
• Squash goes well with ginger, honey, sugar, lamb, maple syrup, nutmeg, olive oil, onions, rosemary, sage, savory, or thyme.
• Winter squash is easier to cut if microwaved for 1-2 minutes. Pierce the squash several times before putting in microwave oven.
• For spaghetti squash: the larger the vegetable, the thicker the strands and the more flavorful the taste.
• Marshmallows also go very well with squash, which I have learned on good authority.

Fairly straightforward, no?