Japanese hentai predates "modern" pornography by quite some time. It is almost always presented in a manga, which is essentially a comic. These mangas are typically erotic, and are all either hand drawn or drawn in some form. There is no live action parts, since it is all in a comic format, which makes it hentai.
Pornography is strictly live action, with actors performing predetermined scripts in a scene. It's quite literally just a movie, an erotic one. Very self explanatory.
My question is:
Which one do you prefer?
[spoiler]Personally, I'm undecided.[/spoiler]
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I find it very strange that anybody would read/watch hentai for sexual pleasure as its essentially a cartoon.