But my number one, all time favorite show -
Buffy the Vampire Slayer. Hands down, fave show of all time. Why? Love a bit of the supernatural, love the storylines. She's the original human who fell in love with a vampire. They stick close to folklore (no frickin' sparkling in Buffy), and most of all, who can argue with a strong, powerful, in control woman! Love the role modelling of the show, love the love story (we all know Buffy and Angel are the real deal, no matter how many Spike and Cordelia storylines you throw in Jos).
I have all 7 seasons on DVD and watch them regularly. Each season has it's own appeal. New characters join, old characters leave, but the one theme throughout it all is that good will prevail. You can't beat that can you?