I feel like writing a thread directly comparing all three of the products, and explaining the features of all three so you can pick what's right for you. Hoping this thread is high-ish on Google to help with newcomers and I was bored.
I don't work for Sonos, so take what I say with an unofficial word.
What differentiates these three products from the Play series?
The Play 1, 3 and 5 are music oriented speakers designed to work purely over WiFi with your favourite music streaming services. The Play 5 features an auxiliary port for using an external device like a phone. But the hint is there - the Play series can't be used as TV speakers alone. If all you're going to do is stream music - consider those instead.
The Beam, Playbar and Playbase are Sonos' home theatre speakers which are designed to work with your TV and also have all that music streaming capability built in. If you enjoy watching YouTube, films, or just making your TV setup be part of the whole-home music scene then the soundbars/systems Sonos offers are an option to consider.
Pros of all three Sonos soundbars over their competitors
One huge perk that no other company has mastered as well as Sonos is a modular system. You can start off with the soundbar alone, add the SUB and/or rears in any order and it'll all work. You can even add speakers to different rooms to have a whole-home sound system for music that works with your home theatre.
It's all wireless, and the only thing you need is enough power outlets, WiFi and a compatible device that has support for the free Sonos app or Desktop app.
Sound quality is top notch, with unique features like Trueplay on iOS which listens to the sound signature of your room and adapts the speakers to work their best. The shape of your room and the furniture within it can really change how your speakers sound and Sonos know this.
It has huge support for tens of streaming services. 55 last time I checked - the most out of any smart speaker competitor.
Why you may consider the Playbar
The Playbar was released back in 2013 making it the oldest soundbar in relation to the others. However, it doesn't mean that it lags behind in anything - it's very powerful.
It features 9 total drivers, 3 being tweeters and 6 being full range woofers. This makes 3.1 sound it produces very accurate and full. Stereo separation isn't hindered in any way.
It's got a bar design, so it's wall mountable.
If you want the wide-open sound of a Playbar, and plan to wall mount your TV this is an option.
Why you may not consider a Playbar
It's only got optical. Industries that revolve around film just don't develop codecs for this as it doesn't feature proper HDCP protocols. You're limited up to DD5.1 for the foreseeable future which technically isn't up to par with DTS.
The Playbar also has a fairly dated design due to its age. It has that classic Sonos look that would visually work best with the Play 1 (not Sonos ONE) Play 3 or original Play 5. Don't let that tell you that it's ugly though! It's still very good looking! It just misses that minimalist mostly black/mostly white finish Sonos have with their newest products.
It's the widest unit at around 90cm wide. Best for larger TV's and lounges.
No HDMI ARC support, AV is 30ms out of sync which isn't noticeable but there, TV remote support lacks fluidity and no built in smart assistants (it still works with smart assistants though).
The price is £700 making one of the most expensive options.
Why you may consider a Playbase
The Playbase was released in 2017, and takes the same approach as a Playbar.
The only main differences are the drivers and form-factor.
It features 10 drivers; 3 tweeters, 6 mid range drivers and 1 woofer. One tweeter is in the middle, and the other two are firing to the left and right. But the mid-range drivers are front facing only and the woofer is deep in the unit with a bass port behind the left side of the grill at the front.
You don't plan to wall mount your TV, but want something that fits snugly under it, that can also support it, that sounds great - this is a great option!
Why you may not consider a Playbase
Well, you can't wall mount it at all and if you do it will simply look horrendous.
Still has that optical connection only that the Playbar has.
Stereo is objectively worse than the Playbar, but it's still very good.
No HDMI ARC support, AV is 30ms out of sync, TV remote support lacks fluidity and no built in smart assistants (it still works with smart assistants though).
It's also quite wide coming in at 72cm making this best for larger TV's and lounges.
The price is £700 again, so like the Playbar it's one of the most expensive options.
Why you may consider a Beam
The Sonos Beam is Sonos' newest product. Actually, as of writing this article it wasn't out yet but I have plenty of information to help you decide whether it's worth a pre-order.
The Sonos Beam is Sonos' cheapest product coming in at £400.
It's got the smallest form factor of all three units, making it perfect for smaller TV's and bedrooms coming in at 65cm wide which is also 2/3 the width of the Playbar!
It has HDMI ARC which allows for perfect AV sync, and the most fluid remote control using your existing TV remote.
The built in Smart assistants also work with HDMI ARC for TV control with your voice.
If you decide to use optical, there is an included adapter.
Why you may not consider a Beam
It's the smallest, which objectively compromises on Sound quality and stereo separation. Sonos tried their best by adding passive bass radiators to the unit, but it simply won't sound as deep or wide as the other two options.
It only features 1 tweeter and 4 full range woofers. Two of the woofers fire to the left and right for partial stereo separation. This unit sound have good stereo separation - but not as good as the Playbar/base.
It sound sound a LOT better than a Sonos Play 3, but not close to a Play 5.
You want the boldest sound from a soundbar, then this may not be the best option.
Still only up to DD5.1. However, it's HDMI and Sonos can add this in an update so keep yourself informed!
That wraps it up. If I made any mistakes let me know.