I feel Manga is more geared towards mainstream mass produced stuff. 20 or 30 titles published weekly in large magazines. The focus is on quantity rather then quality. Though their is good manga out there, their general ethos seems to be publish as much stuff as possible for as cheaply as possible and the good stuff will rise above the trash.
European comics are more artsy. More focused on putting out a smaller but more “high art,” product. Some the most detailed mind blowing art I’ve ever seen has come out of comics from places like France and Belgium. They tend to collect their comics into 48 page hard cover books rather then manga’s 200 page takebons or US comics trade paperbacks. In short quality over quantity.
American comics seem to be at a crossroads to me. They are to expensive to possess the role of disposable entertainment that it once had. But I don’t feel the level of art is quite at the level of European comics(their are some exceptions of course). In short I’m not sure what American comics are trying to be right now.