Simmons Competitor is a term used to refer to two of the leading mattress companies in the United States, Serta and Sealy. Both companies have been in business for over a century and are known for their high-quality mattresses. Serta was founded in 1931 and is now one of the largest mattress manufacturers in the world. Sealy was founded in 1881 and is the oldest mattress company in the United States. Both companies offer a wide range of mattress types and sizes, making them popular choices for consumers looking for a comfortable and supportive sleep experience.