Soundbars and home theatre systems both improve your TV sound, but they are made for different users.
A soundbar is compact, easy to install, and perfect for modern homes. It gives better audio than TV speakers without taking too much space.
A home theatre system offers a more powerful surround sound experience. It is best for users who want a cinema-like setup at home.
If you want simple setup and clean design, choose a soundbar. If you want deeper surround sound and have more space, choose a home theatre system.