If it's a series i really like i'll do both, but i prefer to read the manga's.
Color and sound are nice and the music also makes a big impact on the animes. but alotta animes stretch episodes out its anoying, some anime's have 10 or more episodes per manga. others only 1 episode per manga.
With manga you can go at your own pace, and you can read it whenever you want. personally i enjoy listening to music while reading manga's.
so which one do you like better reading the manga or watching the anime?