Opus is a free and open source lossy audio coding format developed by the Xiph.Org Foundation and standardized by the Internet Engineering Task Force, designed for efficient low-latency encoding of both speech and general audio. Due to its lower latency relative to other standard codecs, Opus finds specific use cases in real-time interactive communication for low-end embedded processors. Opus replaces both Vorbis and Speex for new applications.
In listening tests around 96 kbit/s, Opus shows slightly superior quality compared to AAC and significantly better quality compared to Vorbis and MP3.
That’s what I do for all my music. I go from FLAC to Opus, store it both a NAS and on the phone, and I get the same quality with a very small size for the files.
Also Opus 160 kbps and more is supposedly an “archival” mode where you cannot hear the difference. It could be my last audio format till the end of time.