The phrase "first classes" can be substituted with a variety of synonyms that convey the same meaning depending on the context. For example, "top-quality," "excellent," "outstanding," or "premier" can all be used to describe something that is of exceptionally high quality. Similarly, "top tier," "elite," or "exclusive" can imply that something is reserved for or limited to the best, most accomplished individuals or groups. "Number one," "leading," or "primary" can denote that something is at the forefront and holds a position of prominence or importance. Overall, using synonyms for "first classes" can add variety and depth to one's language and communication.