Blu-Spec is NOT a format. It's standard redbook compact disc on a disc of supposed better quality and data writing with more manufacturing precision. It plays on any player that plays compact discs.
SACD is a high resolution format that requires a player that can play SACD discs.
If one started with an analog recording or a high resolution digital recording, the SACD would probably sound better* because it's a higher resolution format.
The previous post conflates blu ray disc (the video format the also had audio-only releases) with blu-spec cd.
* - some people will suggest redbook cd and SACD will sound equally good and/or standard redbook cd is sufficient to capture all the data in a recording.