To answer this question, we'll need to explain the difference between a smart speaker and a Bluetooth speaker.
While both can connect wirelessly via Bluetooth connection, a smart speaker is designed with voice assistants in mind. While a Bluetooth speaker can play your favorite music, audio books and other audio-based entertainment, a smart speaker will be designed primarily for use with Amazon Alexa, Google Assistant or any other AI-based voice controlled assistant.
Bluetooth speakers, depending on the model, will usually have better hardware inside designed to get the most out of multi-layered audio tracks. Some will even support surround sound or have improved sound support technology that improves the quality overall.
Smart speakers, however, will feature lighter hardware that provides a great mix of sound quality and versatility for voice assistants. If you're hoping to listen to your favorite tracks at their optimal levels, a Bluetooth speaker with audio-enhancing features and tech will be what you want to look for.
If you're just looking to grab a solid speaker for use with Amazon Alexa, however, then a smart speaker will do the job and then some.