I usually post a comment out of curtsey , anything that's on my mind about the comic, even if it's a simple "<3". Because I know comments hold higher appreciation to creators than "Likes" (I also give a like too 6w6). I also do this to follow the "do for other which you want done for you" motto, atleast in pitiful hopes to bring up a louder community of readers. Comics that I'm more invested in I will habitually comment on most-to-every page to show that I am a living-active reader supporting the creator's work, because, well, it's difficult imagining the appreciation of a silent reader on the other side.
I post longer comments sometimes to comics to episodes I find extremely touching (only if I have time though).