"The Quality of Mercy" should probably be watched, because when its A-plot is referenced later on in the series, it's almost incomprehensible without having seen the episode. I have an incredible soft spot for "The Parliament of Dreams," too, and "Deathwalker" gets a fairly important callback.
"Believers," however, is just so incredibly ham-fisted. It's got all the subtlety of a sledgehammer slamming into your skull, as though the script was originally titled "Baby's First Ethical Dilemma" or something.
I completely agree. "Belivers" has always struck me as a story that would have been more at home on TNG than Babylon 5. The scene between Sinclair and Franklin in the Rock garden in particular. I was SEEING Sinclair and Franklin, but I was HEARING Picard and Crusher.