My favorite series is at present a tie between the Wire and Buffy.
Breaking down series I've thouroughly enjoyed past that needs some categorizing.
Gone too soon: Dollhouse: The actor who plays Victor really sells the concept of the series (fantastic actor Enver Gjokaj). Alot of what's great about the series is improved by the pace and unpredictable way the story moves (a stronger feat considering a flashforward midway through)
Pushing Daisies: Subverts the classic will they, won't they trope quite well, is presented like a Dr. Seuss series in live action, which really helps offset and contrast how grimm some of the subject matter is (main character commits manslaughter as a child using magic in the first ep.)
Young Justice: one of if not the best animated series about superheroes I would say I've seen to date, doesn't talk down to the audience, makes me care about and want to see more of characters created exclusively for the series, 2nd season approached politics and media influences far better than many live action series in my opinion.
Favorite sci-fi: Farscape: arcs out perfectly across the series for overall narrative and characters journeys, quality in terms of writing/ effects improves each season, capped off very well with a miniseries.
Current favorite: Hannibal: Season 2 leaves you wondering what will happen next every episode, which is no small feat. Hugh Dancy and Madds Mikelson give phenomenal performances.
Plenty more I will need to add when time permits