Huh, of the actual porn games...
I don't know if it's fair to call it my favorite, but I often find myself going back to play
Hentai Sim Brothel. Frank's Adventure and Ana's Quest were fun, and there was another game of that type, Sexy Vacation I think. Of those, I guess I have to give Ana's Quest the most props for having original artwork. Sexy Vacation had artwork used with permission. Frank's Adventure just stole it from hentai erogames. Also Wiesli's minigames suggest that he may have forgotten or not realized that most people are not on cocaine.
I liked Games of Desire's Swimming Pool Monster. Good artwork, a decent level of difficult compared to some of their other "don't get caught" style games.
Mokusa Painting has a fun collection of block-breaker hentai boards.
Here is their website, if you don't mind fumbling around through Japanese, here is a direct link to one of their boards:
http://mokusa-painting.net/b34/b34.html The default speed of these games also make me wonder if Mokusa Painting is also on cocaine. Which, huh, if Wiesli AND Mokusa Painting are both on cocaine, should I be on cocaine? Is that a thing hentai developers are supposed to do?