Amazon Alexa answers back to questions with short and frank answers. Whereas Siri sometimes gives informative answers but they are time-consuming.
Siri is specially designed for Apple devices. Like; iPhone, and iPad. Amazon Alexa is available for a wide range of devices. So, Amazon Alexa is more compatible than Siri
Both devices work as Personal Assistants using a combination of technologies to understand and respond to users' voice commands. Voice recognition technology allows them to work.
Alexa allows users to order products from Amazon. Alexa is having powerful backend support from Amazon whereas Siri does not have strong backend support from Apple.
If you are finding the compatibility then Alexa is having tons of options and Alexa offers a large compatibility support that connects you with multiple devices
The Amazon Alexa voice assistant is free to use, with no subscription fees required. The only cost of having Alexa is the Echo devices.