Here's my litmus test: suspension of disbelief, or how much is required. For stories like Goldenmaster's 'First Contact' series, which I love, that threshold is pretty low. It's all alien worlds with dickgirls and whatever, let the fucking commence. But, for stories that are supposed to take place in our world, the threshold for suspension of disbelief is a lot higher for me. Stepmom and stepson? Neighbors that barely know each other? Roommates? They can't just start fucking. I need to see that segue where they cross that line, agreeably, and I have to believe it. For me in those scenarios, the antagonist has to make a convincing argument to get laid, or else you lose me.
Now, stories about first dates, BF/GF or husband/wife sex, things like that...obviously that barrier has already been crossed. I don't need convincing to believe the storyline. That kind of story is also kind of boring. We know what's going to happen, and we just click through to get to the moneyshot. For me, it's not just the art, it's the story. Draw me in. Make me want to keep reading. I like to play around with creative writing, usually involving sex. As much as I like to write the sex stuff, I enjoy writing the interactions in between a lot more. To my eyes, that's that part that makes a story. Sex is just the icing on the cake, no pun intended.
What kind of stories and comics do I loathe? Well...monster sex, rape fantasies, gore, old man/young woman imagery...anything that contrasts beauty with ugliness. That's not a turn on at all, no matter how good the story might be, but I won't know because I won't read it. But...make what you love first, and what you think will sell second. If it's not fun to build, it's just work, and work sucks.