I like manga plus because it tells toi the whole story, and at the end of the jour it's usually the only medium toi can rely on to be completely "canon" (unless of course it was a novel series ou something similar first). Also when toi read instead of watch, toi can control the pace at which toi enjoy the story.
It varies. It's awesome to see your fave characters off the page and animated, but animé also often have to leave out details ou completely alter storylines that make it worse. If I have a manga I love, I want nothing plus than to see it animated.