..and I mean from all series, where Q made quite an impact in only 12 appearances. I still think of him (it) as an STNG character though.
My top 3:
1. Q Who-A slight edge over All Good Things. The episode was a milestone and very well written.
2. All Good Things..-The best show finale ever.
3. Deja Q-Not far down the list at all, this episode was notable for it's increased humor, an extremely will written story and critical acclaim in the mainstream media, which was still slow in coming at the time for STNG. It was poignant, ironic, and succeeded in making Q a sympathetic character.
HONORABLE mention: Voyager's "Death Wish" -This episode was fantastic, all sorts of moral and ethical questions with a better exploration of the Q.