Each device has its own different size and price, all of them add Alexa to your room and are able to answer to your voice commands. Echo Show also has a screen to display texts and videos. Each one is able to connect via WiFi and Bluetooth, to answer your request and, for example, play music from any connected device. There are also some differences in the speakers built-in every Echo device: while Echo Dot has a more compact speaker with a plug to connect it to external speakers, Amazon Echo has a 360° omni-directional audio system with separate woofer and tweeter for deep bass and crisp high notes. In a similar way, Echo Show has an expansive, stereo sound powered by Dolby; dual full-range speakers for rich bass and balanced listening.
Complete information about the differences between the three devices are available at the following link: