Cheating/NTR (with some caveats)
To me, you can classify most hentai in two broad categories: Depictions of Love and Depictions of Lust. These two categories are not mutually exclusive and what hentai goes in each category depends on you. I am more into Depictions of Lust since well, the whole purpose of hentai is to help us masturbate and seeing lustful acts really helps.
I find that the best Depictions of Lust fall into Cheating/NTR since the character doing the cheating falls into such a lustful state that they are okay with being unfaithful. However, i stay far away from Netori, NTR x Forced, and NTR in which there isn't enough emotional separation from the victim of the NTR (examples: stories where victim finds out and emotionally breaksdown/resigns, stories where an emphasis on how upstanding/loving the victim is to the cheater, etc). This is because the victims emotional grief distracts you since you end up grieving for the victim. Now, if the art is good enough i can look past this, but that would take some
GOD TIER artwork. An example of a Cheating/NTR that i find is good is utu's
Jun-san Sneaks a Bite. The victim is a douchebag so you don't really care about him, the cheater is really horny, and the sex scenes are oozing with lust.
(An aside, there needs to be more cheating x one-night stand hentai. That shit would check all the right boxes for me)
Glasses
There are inanimate objects in life that people associate a trait to. For example, gold chains can be associated with wealth, muscles are associated with strength, and a wedding ring is associated with commitment. I associate glasses with intelligence. And i find intelligence to be really, really sexy.
Teacher x Student
As someone who has lived (and is still trying to live) their life on the straight and narrow, sometimes you need to indulge in the dark side. A teacher giving in to his student's advances (or vice versa) and engaging in a forbidden relationship fits the bill perfectly.
Office Lady
This is similar to the previous point: two co-workers having sexual interactions behind their other co-workers backs fits into the "indulging in the dark side" category. If the office lady hentai doesn't fit that category, the image of a voluptuous woman in a tight dress shirt, tight knee-high skirt, and high heels being bent over and fucked from behind on her desk or against the window overlooking the city skyline at night is insanely arousing.
Dark Skin x Kogal
Who doesn't love a cheery, fun-loving
brown-skin lady?