It depends on what you're looking for in terms of sound quality, how big the room is, and probably most important, the size of your budget. To have an immersive experience you would need the sound sound system or a high end sound bar. More speakers typically means better clarity, thus a better listening experience.
If you didn't know, in a typical set up:
2.1 includes a subwoofer and 2 front speakers
3.1 includes a subwoofer, 2 front speakers and a center speaker
5.1 includes a subwoofer, 2 front speakers, a center speaker, and 2 rear speakers
To get more bang for your buck, you could get an "older" 5.1 or 7.1 setup for the price of some new 3.1-5.1 setups.