[Hatredcopter]

If you've not even begun learning Japanese (as I've gathered from your asking whether to learn hiragana or katakana first), manga is going to be too difficult. But I would say at least pick up Doraemon or some other children's manga and see what you can make of it.

Also, let it be known that the people who denounce textbooks are often the same people who lack the discipline to actually learn from one. Immersion is key to learning languages, but it has to be supplemented with proper guidance - from a textbook or a tutor or a university class. Self-study with Japanese is very difficult, but you if you buy a proper book (such as Genki), you can at least get a grasp on some basics.