It depends.
Streaming of traditional broadcast/cable TV shows means different things.
Hulu (owned by Disney) has the most next-day content from traditional TV of any service. There's also Hulu Plus which does extra stuff.
Peacock (owned by Comcast/Universal/NBC) has NBC content
Paramount+ (Viacom/CBS) has some CBS content. CBS is a tough nut to crack, because the million-year-old man who is in the most direct control of Viacom didn't understand the concept of streaming until MUCH later than the other companies.
You can also find simultaneous live streaming services. Every damned one of them has a "blind spot" of channels that aren't available for some reason or other. Most of these have a recording function that can store recordings to watch later as well, similar to the good old Tivo.
SlingTV, Youtube TV (which is different from Youtube Premium!), Fubo, DirecTV, Philo: These all functionally do live TV for a set package of channels. One of the big differences with these is the sports networks they can show.
As far as Set Top Box Ecosystems, here are some considerations.
ABSOLUTELY EVERY SINGLE TIME BUY A DISCRETE SET TOP BOX. DO NOT EVER RELY ON THE THING BUILT INTO A TV.
Smart TVs will have trash-grade hardware. My guess as to why is that the TV OEM thinks people want to buy a new TV set every couple years. The discrete boxes will usually have better hardware, more RAM, better remotes etc.
Anyway, your choices are as follows:
Roku
AndroidTV (Google)
FireOS (Amazon)
Apple tvOS / iOS
WebOS (remember PalmOS? It's PalmOS!)
Tizen
Roku has a ton of unique content that isn't found elsewhere, including the ability to direct stream a lot of international and religious content. Ruko is also not controlled by a content monolith, so things will sometimes get yanked because Roku isn't always big enough to negotiate favorable deals with media conglomerates. I don't like Roku hardware very much (I think even their high end boxes are sluggish) and I also hate that Roku intentionally makes it difficult to watch content local to your LAN or mobile devices, but it DOES get along well with Google, Apple and Amazon.
Apple stuff basically runs iOS and is also definitely compatible with a lot of things. It has excellent support for high-end displays including both of the competing implementations for HDR video (Dolby Vision and DisplayHDR), but it has limited compatibility with surround sound formats. It's also not super simple to play back LAN-local content through one.
WebOS only happens if you buy LG hardware, either as a TV or a streaming box. Limited app and video source support. I'm not a fan.
Tizen is Samsung's AMAZINGLY stupid Linux-derived smart device OS. Here's the big problem with it: There are three different major versions that Samsung supports. Apps compiled for one do not work on the other two OS versions and you can't change the OS version of your device. Which leads to weird things like having a TV that's two years old that can't get an app version that supports the current login system used by Youtube or Netflix. My parents own a Samsung TV like this. Samsung uses Tizen on some smart watches and basically anything that might have a display. You do not want it on anything. To Samsung's credit, owners of Samsung devices can also access a private set of exclusive content on branded devices that includes a lot of odd, licensed channels, like 24x7 streaming of Spongebob or Scooby Doo reruns, plus a limited amount of real time programming like CNN. I can cast that from my phone or tablet to a non-Samsung TV though.
FireOS is somehing you get on Amazon branded or partnered devices. It's not great because Amazon has a bit of a poor track record with Google services, especially around Youtube, but it's also often overlooked entirely by Apple. Amazon also tends to cheap out on hardware and even the fastest devices are sluggish. On the other hand, the installed base is huge so everything else tends to work fine with it.
AndroidTV is the hardest thing to talk about. Most AndroidTV devices are unacceptable filth that's built using the cheapest possible components, remotes that are a crime against humanity and chock full o' Chinese spyware. BUT in the budget space, there's the ONN Google TV Streaming Box, which is $20 and is a more or less pure upgrade from a standard Chromecast experience, and the nVidia Shield, which supports literally every Audio format known to man and both HDR display formats. They have a really nice remote as well. They also use Tegra K1 SoCs and they have been getting continuous software updates that add features since they were released. Upside here is that they talk to Amazon, Google and Apple just fine. Down side is that they cost more than almost everything else other than an AppleTV.
Generally speaking, all these can do ALMOST anything. Apple has some things that don't work with anything else and Apple and Roku specifically make watching content from your LAN a hassle. AndroidTV might have a hard time dealing with Amazon (Prime TV /Music) content. Amazon will definitely have a sub-par experience with Youtube.
Xbox and Playstation are also in this category and tend to be surprisingly compatible with things, but you aren't buying a 500W, $500 Xbox so you can watch Amazon Prime TV, either.
The formula is making sure that the streaming sources you want work on the streaming device you've settled on. Once you've figured that out, buy one everywhere you put a TV.
