unoconv differ from using
libreoffice --headless --convert-to?
When should one prefer one over the other? Any differences in performance or quality?
unoconv has 2 modes: either you use a long-running soffice process, in which case you get fast conversion or you start a new soffice process for each document, which increases security. You need to choose between the two. soffice --convert-to is similar to the “secure” unoconv mode.
BTW, Online also allows document-conversion and tries to have both speed and security at the same time, you can read about that here.