There is a school of thought that considers canned foods to be a compromise, trading quality for convenience. That's not always true. With tomatoes, for example, the "fresh" tomatoes available for much of the year are hard and flavorless, bred and picked purely for their storage characteristics. In contrast, canned tomatoes are usually picked when ripe or nearly ripe, then processed almost immediately in a nearby factory. Their quality is consistent and their flavor is usually better than supermarket tomatoes. However, if it's tomato season where you live, by all means substitute fresh for the canned.
