Amazon Unlimited vs Apple Music
Siri is the real distinguishing factor, though. I unashamedly use Apple devices most of the time. I am writing this article on an iPad in bed while listening to Apple Music streaming from an iPhone to an Airport Express that feeds my bedside headphone setup. I have an Apple Watch that I use to skip songs or tell it what to play next. I will then add any links to this article and post it from an iMac or MBP. All of these Apple devices now work with Siri. The problem with Amazon Music is that it does not work with Siri.
Location, location, location
(Note: I should mention that I still haven't gotten all of my files loaded up to Amazon because their app is awful and crashes every time I use it.)
The first shortfall to the Echo Dot is that it doesn't have a digital output. This means you are using the onboard DACs vs higher end DACs that you can use with the Airport Express which has an optical digital output.
Also, I now have 3 receivers with AirPlay built in. This means that I can hit one button on my iPhone and my receiver will come on, switch to the correct input, and start playing. It will even show album art, album info, and song information on my TV if I have it on. To listen to the Dot on that setup, I would need to turn on the receiver and switch to the correct input. Sure, with the Dot, I could do that with a command, but it is still more steps to start playing music. In other words, some of the convenience of the Dot would be outweighed by some of the inconveniences.
I should mention that my receiver also has Bluetooth built in, so I could place the Dot near my seating location and send music to my receiver wirelessly. However, AirPlay is lossless and Bluetooth currently uses compression which means the music might sound worse.