1. Q Who
-- Introduces the Borg, showing our arrogance and paying off the reason Q comes to the Enterprise in the first place. I still mutter "It's not safe out here. It's wonderous with treasures to satiate desires both subtle and gross, but it's not for the timid."
2. Déjà Q
-- I love the interactions with Data. The comedy is spot-on. And the end scene both makes me laugh (Au contraire, mon capitain! He's back!") and smile (for Data)
3. All Good Things...
-- Honestly, this was a stretch. I think Q was better before Q-Pid. But he does say something about humanity in this one, albeit heavy-handed.
2. True Q
3T. Q and the Grey