I prefer the manga mainly because the story is more involved and because it doesn't have the, pardon my language, suck balls ending that the anime has. The only thing that bothers me about the manga is that it's pacing isn't that great instead of the nice linear way of plotting it's more like a exponential equation.
This is her way of plotting the storyThis is how it should be. See the difference one's nice and linear and the other is all suddenly jumps upwards. Basically in the manga the pacing is really slow up until recently, where the pace is sunddenly jumped up and all these mayor plot twists and conflicts are thrown in near what hopefully is the end.