I don't watch a lot of current stuff, not for any morally uptight reasons like "it is all crap" that some spout but merely because I lack the ability to follow a strict schedule. As such most of my favourite shows are either things I have watched on my own time/reruns, things that have no structured plot, or stuff I have watched for many years.
Many anime, Corner Gas, Clone High, Family Guy and Futurama fall into both the 1st example and a bit of the second.
Mythbusters, 22 Minutes, Colbert and the Daily Show all fall into the 2nd.
And the Simpsons I have loved since I was a little kid and I continue to watch it despite what the rest of the world has to say on the matter. I'll admit I don't watch a lot of the newer episodes when they are new, but this is due to my inability to follow a schedule. There is a website in which I can catch up on them though so it isn't a big deal. Most of the treasured memories of the show I have on dvd sets anyway.
However, this turns into more of a "This is what I watch" rather than a favourites list mostly because I can't really pick a favourite.