Roku is excellent because of its simplicity, tidiness and imho software quality, which is why I said it's probably the best if you care about ease of use. I find it takes the least time to start watching stuff, requires the least button clicks, and there is absolutely nothing you have to think/worry about or do after you set it up, which takes maybe a minute. You still have access to pretty much the same apps (they call them "channels") though, and buttons on your remote to 1-click access them. There isn't much to explore other than settings for your TV and some themes, but that's the beauty of it to me, as I wouldn't want my TV to feel like a Smartphone. I agree it's about personal preference, but to me, or if I was buying a TV for a family member, it just feels like it's the closest to what I'd want from a Smart TV OS.
I really like Roku, but one of the reasons is because I also don't like how bloated and messy Android TV feels. I feel like while Roku offers you an easy way to navigate to what you want to watch, Android TV bombards you with all sorts of random stuff from different apps and dozens of video recommendations as soon as you turn it on, and I don't like feeling like that on my sofa as soon as I turn on the TV.
It has never been a 4-way race. As a matter of Fact, Vizio is not a major TV maker - they are US-only, and generally, that's because they were traditionally too bad to even sell in other countries (or US Walmarts to be specific). The first time I HEARD of them was when I traveled to the states a couple of years ago.
There are many brands coming and going. Just a decade ago, Panasonic and Pioneer were the best TV makers. The market changes constantly.
TCL is a Chinese company for sure, but it's making incredible TVs that Visio or LG can't hold a candle to (in LCD terms, LG's OLEDs are a category of its own) and Sony and Samsung's best are generally competitive with (in terms of image quality, definitely not price).
Sure, LCD isn't as amazing as OLED, but the R615 does FALD well, the color reproduction and contrast are excellent too, not to mention that it does HDR very well - it's as close as LCD has gotten to OLED and I was very pleasantly surprised by those TVs. Basically, it's either that for $700, or an OLED if you can drop 2k, with pretty much nothing worth the money in between. Heck, you can drop $1500 on a Sony 950 series and you'd be essentially getting a R615-ish image quality.
While OLED is definitely better, image retention is still the largest problem. I didn't go for OLED for my TV just because of that discomforting feeling that the image deteriorates with every hour I have it on, and you can't stop it. That said, differences between individual models are often academic, with $4k models rarely being worth the money over $2k models, unless you absolutely have all the money to burn on a TV that might last you 3-4 years, as it's still unlikely an OLED TV will last you as long as a good LCD would. As in, that $700 LCD will most likely look better in 3 or 4 years.
The thought is that I'd definitely prefer not having to use it. If you have to due to range constraints, I am not in the loop about which one is the most reliable. I have no idea how their mesh solution is, but I trust Netgear stuff as a rule of thumb and get them whenever ordering blind and never been disappointed. Speed tests and reviews aside, I had three of their routers over the years working 24/7 as my main routers and never in my life had one drop a connection, not to mention never needing to restart one.
That said, mesh networks introduce difficult technological challenges so I'd do my research on the specific product before getting one.
edit: oh, it looks like they're the best at mesh too, and I'd wager an uneducated guess the most reliable too:
https://www.tomsguide.com/us/netgear-orbi,review-4263.html