Comments!!! But I do love likes. Both keep me motivated to keep going.
This is exactly why when I view others' work I try to leave a comment on something I noticed/stuck with me. Comments are free and people like them. And I'm usually a busy body anyway. The only time I don't is if I end up seeing it while I'm out running an errand or if I'm in the middle of cooking lol.
(though it is harder on novels because usually i save those for when I'm working out, cause my phone reads them to me (I'm dyslexic))