hehe, a thread like this always pops up.
Anyway, I choose manga. Anime is great, especially when you're feeling particularly lazy. Plus the music, voices and animation can really envelop the viewers. Yet I still prefer manga, so much so that it's become almost instinctive. Most of the times it's the transition from manga to anime, like book to film, that I dislike, since producers skip parts, place more emphasis than needed on others (like fanservice), or create new material out of nothing. It's kinda ruined some series for me, thus resulting in a very disappointed Raymond.
That said (if it made sense), my judgment can't really be passed upon series that only have an anime or in which the anime came first. Which is fair, cause those are usually great to watch.
But I still prefer manga :)