Manga represents comicbooks or graphic novels from Japan while Manwha is from South Korea.
I personallly prefer manga since the artistic drawings are generally more pleasing while manwhas have generally unporportional people. Also Japan's point of view of the world definately show in their work. Portraying grouped indiviuals in an environment. But I do not deny that there are very outstanding Manwhas that I personally like Park Sungwoo who drew Legend of the Eight Dragon Gods, Chun lyang Yul Jeon, Now, Black God and more. His art is very beutiful. Also I like a Manwha called UnblanceX2. It is a love story of a teacher and student. It is also drawn pleasing similar to Sungwoo's work. Japan's manga industry is very advance unlike the American paper comicbook companies. American comicbooks are loosing interest since it is mostly about superpowered heroes with amazing steroid muscles which is unpleasant mostly. Also storywise it is the same theme of heroes defeating villans with not much emotional dramas and most of the time the stories fail to continue as in tv episodes. If the stories continued with new kind of stories and the price of the thin paper comicbook goes down I believe American comicbook industries may have a chance for come back. Otherwise it would be overrun by Japan or Korean comicbooks.