Porn is always the same, it has no real story, you can't get any emotional attachment, the fake tits and the fake expressions are not appealing. And in my subconsciousness I remember while hentai characters don't exist, many porn actors/actresses have a shitty life, one reason for it being the decline of their salaries over the last years. There are some good porn companies like, as mentioned on this thread before, X-Art, which has really appealing actresses that (at least seem) to completely work out of their free will, and this can be a reason for them to put in more effort in their job, what also raises the qualty of their films. I am not an expert on this matter, but I think that most hentai artist are doing their work not only for money, but also because they have fun at what they are doing, the porn industry today is only making as much money as possible by delivering generic products.
Hentai, what I consider as an art form, a category normal porn used to belong to to a certain extent due to its creativity it expressed in the time until the 80s, has a natural advantage towards porn: due to its form it allows an almost endless creative potential, the artist have more freedom, whereas the porn industry is forced to set its focus to the mainstream market. Hentai also does a great job at delivering a wide range of emotions to the reader, sometimes the reader can empathize with the characters. What I also like more is that hentai can also have a good story, something I per se don't expect from a medium that people mainly use to jerk off, but nevertheless HIGHLY appreciate. As mentioned already, the emotional aspect is a big reason for me why I like hentai more. Porn, at least what is today released as porn, is in my case unable to cause any emotions within me, something what (most) hentai can. This aspect makes it possible for the reader to put more attention into the medium he/she is consuming, what causes the reader to have a higher opinion on this certain medium than something he/she has not "invested" emotionally.
The biggest advantage of hentai towards porn is that it can depict what porn can't due to the natural limitations of real life. It cultivates and sometimes even creates certain non RL-applicable fetishes, like monster girls in my case. Due to its openness everybody can find his/her niche easily.
At last I really appreciate the work hentai artists and mangaka in general invest in their creations, in many works you can really see the devotion that was put in it. I don't want to say that porn direcors/actors/actresses don't do jack shit for their films, I just want to say that a lot of them see their job as ......well, a job where they just do what is required and don't put extra effort in it.
In the end, I prefer hentai way more than porn, whose industry should redefine their priorities and their way of work, what seems like a wish that will never come true because in my humble opinion the porn industry is one of the most capitalistic branches that currently exist.
P.S: sorry for eventual grammatical or spelling errors due to me being from a non-anglophone country. I am studying English at my university (for becoming a teacher) so my further posts will be of higher quality.