Hello @ObieO, welcome to Sonos Community!

I believe it really depends on the usage and personal preference. If the 20x15 metric is in feet, and please correct me if I’m wrong, I think the Sonos Beam(Gen2), Sonos Sub Mini and the two Era 100’s would be a better fit.

The surrounds improve the overall Home Theater experience and you can also set the Music Playback setting to full and fill your living room with music.

On the other hand the Sonos Arc and Sonos Sub (Gen 3) bundle is a great start if you spend a lot more time watching TV than listening to music and you can always add the surrounds later on if you feel like it.

With my response your thread jumped to the top of the activity list, maybe other Community users can share their experience and help you decide.

Thanks for the response @Sotiris C. ! 
 

I would say it would be about 50/50 between movies/tv and music. The sound bar will be mounted under a 70” tv as well if that makes any difference. 

Hey @ObieO,

For a TV of that size, allow me to change my recommendation! 

The Sonos Arc will give you a better stereo separation, comparing it to the smaller size Sonos Beam(Gen2) under a 70’’ TV.

Have a look around in our Community, there are plenty of threads in regards to mounting a Sonos Arc that you might find helpful.

I got as far as “open concept” and instantly said Arc and Sub. I’d add Era 300 surrounds as budget permits.

I had a Beam and Sub in my open plan room and while the bottom end was great the Beam really didn’t fill the room.

I also find the stereo imaging from the wider spaced Arc speakers is better than the Beam in that room. In a much smaller room I’m happy with the Beam.