Before refrigeration was common, people would say you should buy oysters only in months with an "r" in their name -- that is, September through April. Shellfish spoiled quickly in the summer.
With tomatoes, the opposite is true. Summer tomatoes -- fresh, ripe, locally grown -- are unrivaled in color, flavor and juiciness. Most winter tomatoes in the supermarket were picked green and force-reddened (not necessarily ripened) for the journey from the farm. They're more durable than flavorful.
If you must have fresh tomatoes out of season, greenhouse-grown are reasonable replacements. They're increasingly available year-round, but higher production costs make them more expensive.
If winter tomatoes are destined for cooking, opt for a good-quality canned brand. With high-tech processing, they retain more appeal than their "fresh" counterparts ever had. Choose whole tomatoes -- chopped or diced forms might hide second-rate pieces.
Next, we look at choosing the cream of the crop.