I haven't played Final Fantasy 6 so can't say anything about that. FF7 does have a stellar soundtrack, 8 is worse but does have a few good tracks, FF 9 is unimpressive, Final Fantasy 15 only has good combat music - the rest of the soundtrack is pretty bad imo so I just ended up listening to FF7 instead.
I really would have to say for me, it would be the music from the Final Fantasy-Crystal Chronicles- and what really makes the music so unique, is that the tracks are played using ancient instruments-some from the Medieval and Renaissance times, like the crumhorn and hurdy-gurdy !
Final Fantasy X - To Zanarkand seems to be the good song. And it's on youtube too. So you can give it a listen. FF 7 remaster also has remastered sound. So worth listening to those sequels and remastered.