the first element really has to be a spontaneity that comes to me and is worth getting down.
after that, flow and some kind of narrative continuity are what i prize the most. Lyrics and melodies can be dome a dozen and of course there's going to be small things in there you're proud of, but what i look for most is a way to make the song cohesive and fluid.
being memorable just means it worked well! it's hard to write something and make it memorable from the start, that's an aspect that goes with a really good riff. if the song is cohesive then the memorableness of your hooks and the ways you string them together combine to make a great song!