I like anime that tend of have something out of the ordinary, the closest way to describe this would be: experimental. Those that try new approaches and give something new to learn from. After watching around 150 different series more or less completely, anime tends to become quite repetitive if you watch everything that comes out year after year. But sometimes, a certain animation group and production team seems to try something that hasn't been done.
I could probably watch any genre that is positive, negative, dark, humorous, physcological, for girls, action packed, horror, gory, etc and still like it. It all depends on the approach of the genre and the story that this anime has to tell. Most of the classics or titles that pop up in most of the top 10 lists generally hold something original in them. I guess it always depends on my mood mostly. Light and funny if I'm feeling down and downright turbulent in every imaginable way for the human spirit when I'm energetic and ready to stand in front of things that make you think. A quick example of a few anime of light and funny quirks:
Excel Saga FLCL Ouran High School Host Club Slayers Love Hina Oh! My Goddess (though with something more profound within this one...for me at least)
Gunsmith Cats (the manga was hilarious)
Sailor Moon
etc........(I could go on for too long)
As for more darker ones:
Serial Experiment Lain Ergo Proxy Elfen Lied Ghost in the shell Noir Neon Genesis Evangelion Wolf’s rain (at some point it gets strange)
Witch Hunter Robin Jin-Roh Higurashi no Naku Koro ni
etc....
Last thing I watched was
Welcome to NHK, I thought it wasn't bad and talked a bit about Hikikomori and it felt more realistic than most of the other interpretations of such characters in other anime series. Just for that, I thought it was very interesting to watch, though it didn't affect me enough to be put in my faves list. Last thing I really liked must be
Black Lagoon. This series mixes action, psychology, humor, quite a few bits of blood, twists and well, ORIGINALITY!!!....I think :P
I could go on, but generally, originality and a good delivery of something basicly sets me up for going along the whole ride of an anime series/movie/voa/etc...