Number of channels and speakers
If you simply want to improve the sound from your TV, a soundbar with 2.1 channels might be all you need. However, for even better performance when watching TV/movies and listening to audio, a 5.1 or 7.1 model might be a better choice. 5.1.2 or 7.1.2 models support Dolby Atmos, which is designed to produce a more immersive experience by angling speakers upwards to the roof to simulate sound coming from above.