Ecosystem guide
Amazon Alexa devices in my home.
The broadest device compatibility in the market. If it has a chip and a Wi-Fi radio, it probably works with Alexa.
19 devices personally owned & tested
Alexa's biggest advantage is reach. No ecosystem comes close on the sheer number of compatible devices, and Alexa routines remain the most powerful and flexible automation builder available without writing a line of code. I use Alexa primarily for voice commands in rooms where an Echo is already present and for devices that work better on Alexa than on HomeKit.
Everything on this list I've personally tested with Alexa — not just "certified Alexa compatible" but actually paired, voice-commanded, and run through automations. If something was unreliable or required too many workarounds, it didn't make the list.