Choose one, choose all--I'm not going to dictate ;)
While none of these are exactly my favorites overall, I quite like "Dead Man's Blood" for putting the Winchester family dynamics clearly on display. And I must confess I have a kind of fondness for the poor, failed "Bloodlines", which tried too hard and just utterly flopped. There was some potential to it, but it got jammed too hard into the backdoor-pilot slot and got mangled in the process. "Angel Heart" made me actually feel sympathetic to Claire instead of merely annoyed, which is a pretty good trick, while "Don't Call Me Shurley" is a pretty impressive piece of writing, giving us a style of episode we hadn't seen before, even 11 seasons in.