While I don't have an Iliad for reference, I have converted quite a few manga for viewing on my Reader and cannot really complain. While some may bring up the issue of the low grey-scale table, this is really a non-issue with mangas though may pose a problem with color comics, depending on the downscaling used to when converting them to grey-scale. When it comes to prices vs features, imo the Reader takes the Iliad as it is fairly lower in price, has the benefit of a much greater battery life, and has instant-on. When it comes to screen size, the Iliad has the Reader beat; wish Sony marketed a larger screen version, esp. for my PDF's! But until then the Reader will have to do.
BTW In regards to manga, the predecessor to the Reader, the Librie was designed with manga in mind. However, if you want to view American-size comics, your best bet may be the Iliad; though I'll stick with my TabletPC (esp. in regards to cost vs features) for this and wait for a larger, color screen version of the Reader for that.