I like the Fire TV platform. We use the Cube with ethernet. IME, this is much faster than any stick on WiFi. It's extremely snappy and responsive. Yes, the homepage can be a bit "pushy" on Prime and sponsored content. Sometimes this is annoying, but often it is helpful. Overall, I like the homescreen look and layout, plus some short-cut functionality, like bookmarks for the Silk browser. This is how I look at weather radar. We also use the Live Guide from the home screen. And DW likes the "Continue Watching" feature.
The Cube is also an Echo Show device that uses your TV screen for the visuals. So we use it for home automation stuff using the mic button on the remote. For instance, we can pull up a live view of our 3 outdoor Wyze cams, turn lights on and off, unlock the front door, etc. If you ask about the weather, you'll get a forecast display on the TV. When you ask it to play music, you get visuals of the artist, lyrics, etc. And of course, you can check the status of Amazon shipments, which will display an image of each item and it's expected arrival date and time.
I also like the integration with Amazon Photos. I know that other platforms do this as well, like Google Photos on Chromecast. But it has become our main way of looking at photos. Our phones automatically upload to Amazon Photos. So as soon as we get home from an outing, we can enjoy our photos on the big screen. You can also search for specific photos or image content using voice prompts.
The remote is intuitive and simple to use. It controls the TV and our AVR. You can change inputs with the mic button and voice prompts, though we rarely do that. We don't use any other remote.
Roku is a simpler display, less cluttered, easy to use, and less "pushy"... though not quite as agnostic as it once was. Personally, I like some of the added functionality and the linkage into the Amazon ecosystem. Certainly Apple TV links to the Apple ecosystem and Chromecast links into all things Google. If you don't want any of that, then Roku is the way to go. Or just use the smart apps on your TV, which BTW are MUCH better than a few years ago. Otherwise, pick your favorite ecosystem and enjoy the added functionality.