Tough call on the worst. I've looked over the episodes and can't find one that I would refuse to watch again.
"Death Knell" (which I still thought was very good) would be the one that I would consider the least 'comfortable.'
There were weaknesses in some episodes:
"Grace" was a little hard to follow, but a very attractive episode.
I think "Heroes" could have used a little more explicit footage of Janet's fall.
"Lost City" had the biggest oversight -- Daniel was NOT the only one who could speak the Ancients' language. Jack and T'ealc had spent weeks mastering Latin in "Window of Opportunity." Maybe they were a little rusty, but they could have managed.