Thank you!
tl;dr: Either for now will work. I'd recommend Benben if you need more VGM support, want to use certain foramts (.xspf, .jspf, .sid, MIDI, music out of Doom WAD files), or if you want an AppImage. Otherwise, I'd recommend Aika.
For a comparison table: https://fossil.cyberia9.org/aika/wiki?name=Relationship%20to%20Benben
Longer answer:
Benben still supports more stuff at the moment: playlists, MIDI, C64 SID files, WAV and Au playback, Doom WAD files, more comprehensive VGM support, XSPF/JSPF playlists, remote control... So if you want any of those features, stick with Benben. Also stick with Benben if you want to quickly convert to WAV or Au, 'cause that is not in Aika's future.
At the moment, Benben also has a working reverb and stereo expander effect. Aika does not yet have these. Howerver, Aika v0.1.0 will support an equal loudness curve effect, which Benben will not have.
However, Aika will eventually support all the same formats. It already supports most of them (mp3, FLAC, Opus, Vorbis, WavPack, QOA, XQAF, and some VGMs). It also uses a fraction of the RAM, is *much* easier to build from source, can be extended with plugins, and is slightly faster. But, it's not possible to distribute Aika as an AppImage, so you're stuck compiling it from source unless you're on Haiku. But, if you just play MP3s or FLACs or whatever, Aika will probably give you a nicer experience.
Benben will also eventually become just a tool to convert to WAV/Au once Aika meets or surpasses all of its features. So keep that in mind. But that'll take quite a while.
