First off the Amazon Fire TV has been discontinued, and the Amazon Fire TV Stick (and 4K) is the current device. The stick is a dongle that plugs into an HDMI port to provide streaming video from some online sources. There is also the Amazon Fire Cube which is similar to the TV but with some of the Echo features built into it. Content comes from Amazon as well as apps to bring in other content. You would have to read up on the ads elsewhere.
None of the Amazon devices support Dolby Vision, as the Cube doesn't even support UHD, and the Fire Stick 4K can't handle the processing.
Apple TV has been upgraded to 4K with Dolby Vision. The older version is probably still available, but is limited to HD. Content comes in through apps from various sources, and you can use it to buy and rent content through iTunes Store. The older version of this I saw did not have ads appearing, but you will see promotions if you access the iTunes Store. It is like having an iOS device connected to your TV. Because it is integrated with your Apple ID, it can access your iTunes content, iCloud content, and more.
Just because a reviewer didn't mention Apple TV doesn't mean there is something wrong with it. The reviewer may have been limited to the dongle form factor, Android OS, or cheap devices.