Such a personal, individual matter, I think.
Over many decades, and in many countries, I have meditated solo and with groups numbering from two or three up to twenty or thirty and more.
Question is, what is the purpose or intent in the mind or minds of those involved. So many potential spiritual tasks.
Solo, I go for
uninterruptable silence.
In group work, I have always encouraged using
sound. The larger the group, the more difficult it can be to decide on what sound.
For therapeutic purposes, whether animal, human or planetary, I favour the sound of combined human voices as in "OM-ing" and "TONE-ing." With both these practices, I have encouraged accompaniment by 'live' wind instrumental music.
In the latter case, my personal preference is the Aboriginal didgeridoo. (Google that for examples.)
The last time Joyce and I did that was at Uluru (Ayers Rock) in central Australia, with about forty others of various nationalities, under a fabulous starlit sky, back in November 2004.
L & L