I prefer reading manga i think...it's always the best n original...
they alter some content from manga in anime myb thinking it's a much better ending or suitable view for us n also because due to limit number of episode they can do in an anime..though mostly they messed it up.
Take Fate/Stay night for example...all the best inspiring quotes can be taken from the manga bcoz the anime is totally...how should i say it? off track? In other words,it-the anime- totally downgraded the quality of the manga's plot.
But not all anime totally bad,some r quite good n have a good ending better than the manga. I repeat,SOME. lolz.
But sometimes we just dont want to spoil our eyes or making our hands tired from scrolling down manga pages online which is y we chose to watch anime.
Firstly,it summarises it up.
Secondly,the pictures/characters are moving unlike manga which is still pictures.
Thirdly,the characters can talk! like real talk with sound effects n all that especially when u r watching an action anime like naruto or d-gray man or one piece or heart tearing anime like full moon wo sagashite or music anime like la corda d'oro.
Anime makes these manga come alive on screen...it would b better with sound effects..
u cant feel the story sometimes without sound effects or voices especially the manga that revolves around music. Can u imagine reading such manga but u cant hear the bckground music that entices the audience or the music that the characters play in the manga??
So basically it's ur choice..but for me,I usually do both. reading the original manga n watching the anime. To get the best of both sides.
