Both, depending on what situation I'm in (sounds quite serious).
I used to prefer manga as I can stop whenever and read it wherever I want, while anime is more time consuming and you need to watch it continuously. Anime wins on being funnier with sound and movement. Manga is sometimes better for some series, for example Kuroko no Basket, as you can see Kuroko's movement clearly.
I used to rarely watch anime and spend majority of my time on manga. But when I moved to the UK, it is extremely hard to find a manga, if there is, they are not up to date and very expensive (Manga in Thailand is less than a pound, around $1.5 each and they are everywhere). So this kind of forced me to start watching anime.