My criteria was, if I was watching the entire series do I have the urge to skip this episode.
S1: 28/29 - 96.5%
S2: 22/26 - 84.6%
S3: 20/24 - 83.3%
I would rate Season 3 Episode "The Empath" as the worst episode. It is a snoozefest! I can watch and enjoy pretty much every other episode, but it take effort to get through "The Empath."
That was my criteria too. We're pretty close on the number of episodes we like. For me, the very last episode, Turnabout Intruder, is the worst.