It's an odd thing, but in all the years that I've been writing professionally, and having worked with so many others who have done so, I've found that as songwriters we are the worst judge of our own writing. Some of the songs that I feel are my best work don't seem to move the needle for other people, and yet songs that I wrote and hardly gave a second thought to wound up getting recorded.
I think after a while you "know" that you've written something good just by comparative analysis...how does it stack up to your best work.