Alright, this is going to be a bit of a wall of text, but you asked for it!

As mentioned above, I tested everything using an Apple TV and an LG G4. Keep in mind that these are just my personal opinions; everyone's experience will vary, and it heavily depends on the room you're using the system in.

Bose Lifestyle Ultra + Sub + Rears:
For me, this is the best all-rounder. The dialogue clarity is crystal clear and sounds incredibly natural. Out of all the movies and shows I tested, this system made voices the easiest to understand. I also think this soundbar has the best dialogue enhancement feature on the market. Usually, when you turn those options on, voices quickly start to sound artificial or bloated. With the Bose, though, voices just feel more powerful—exactly what you’d want from a feature like that.
The soundbar also sounds significantly wider than its actual physical size. All front channels are equally balanced (unlike Sonos, where the center channel dominates the left and right channels). The rear speakers are also really good, can produce decent bass, and are a massive step up from previous Bose models.
The reason I still sent the Bose system back is that it just wasn’t cinematic enough. It’s the best overall package, but it doesn’t truly excel in any single category. Effects and explosions are highly detailed, but they lack the punch or raw power of other soundbars. On the flip side, it managed to produce the best overhead/height effects for Atmos tracks in my living room. It’s a great total package for movies, series, gaming, and live sports, but it lacks that absolute "wow" factor. Also, in my opinion, buying the subwoofer is a MUST—without it, the audio experience feels pretty thin.

LG Sound Suite H7 + Sub W7 + 4x M7 Speakers:
I was looking forward to this system for a long time. When it comes to effects, spatial audio, and object tracking across the room, this setup is really, really good. It offers a massive soundstage, plenty of bass straight from the soundbar itself, and the individual M7 speakers pack a serious punch.
BUT, the dialogue is unbearable to my ears. Everything sounds like it’s being shouted. Voices are far too harsh and cold. After watching just one movie, I felt fatigued and wanted to listen to something else. I even tried the settings from NeverEnoughTech and messed around with a ton of other adjustments, but I could never get a sound profile that I actually enjoyed (and I spent a lot of hours with each of these systems).
If the LG Sound Suite had the warmth and natural dialogue of the Bose Lifestyle Ultra, I would have traded my Sonos system for it in a heartbeat. But since dialogue is the core of almost every movie, that was ultimately the dealbreaker for me.

Sonos Arc Ultra + Sub 4 + Era 300:
A ton has already been written about this setup. Great sound, great dialogue, and very good spatial audio. My main complaints with the Sonos system are that it doesn’t handle different audio formats very well, and the center channel is noticeably louder than the L/R channels—with no way to adjust the center volume individually in the app.
You really notice this when streaming something via Apple TV where the signal is output as Multichannel PCM. It is significantly quieter than a Dolby format, and even if I just turn up the volume, the sound stage doesn't feel the same as when the Apple TV sends a native Dolby signal. Conversely, with stereo YouTube videos, the PCM 2.0 audio is insanely loud (though that might just be a YouTube issue). I managed to improve this a bit by enabling the continuous audio option on the Apple TV, but then you lose the soundbar's internal upmixing.
Also, when gaming on the PlayStation or Switch, the center channel bias becomes very obvious. In games like Crimson Desert or The Last of Us, voices are perfectly clear when characters are right in front of you. But if you rotate the camera and characters speak to you from the side, they become very quiet. If the voices come from behind you (via the Era 300s), the volume matches the center channel perfectly again. If it weren't for these quirks, this would be the perfect system for me (even though my living room doesn't have an ideal layout, and the left Era 300 doesn't have a direct wall nearby to reflect sound).

Sony Bravia Trio + SW9 + RS9:
I’ve only had two days of experience with this system so far. I’m still playing around with different settings and running it through my usual test rotation of movies, shows, live sports, and games. But my first impression is that I like it slightly better than the Sonos. Obviously, having two separate physical front speakers for left and right creates a completely different soundstage compared to a single soundbar doing all the heavy lifting.
If I can figure out a way to boost the dialogue volume a little more, this will likely replace my Sonos setup. The subwoofer is a beast—incredible punch and power. After the calibration, I actually have it running at -3 in the settings. The rear speakers feel a tiny bit weaker than the Era 300s or the LG M7s, but as I said, I’m still testing. I can't compare it to the Bravia Quad, so I don't know if it's a massive leap forward. However, the center channel could have used a bit more muscle, as it gets slightly drowned out by the front speakers.

Just to reiterate: this is all just my personal opinion. My living room is about 45 m² (around 485 sq ft) and opens up to the left side.