Hmm, this is a tricky one because 'best' is so subjective, and romance within the genre can mean wildly different things depending on what you're after. Personally, I've always found the stories that try to weave emotional depth into the explicit content are the ones that stick with me longer than the purely physical ones.
A lot of people point to Anna's 'Siblings' as a classic example where the taboo relationship actually has a slow-burn emotional foundation; the tension isn't just from the act but from the characters' genuine, messy feelings. I also think some of the fantasy-themed ones, like 'The Inquisitor's Oath', do a surprisingly solid job. The world-building forces the romance to develop through shared trials, making the eventual intimacy feel earned, not just inserted.
That said, quality is super inconsistent. You can spend hours wading through titles where the romance is just a flimsy excuse. My method is usually to search by tags like 'slow life' or 'slice of life' paired with the adult tags, which filters out some of the more aggressive, plotless stuff. The ones that get serialized and have fan communities discussing them often have stronger narrative bones, like 'Café with Ghosts' where the romance is bittersweet and central to the mystery.
Finding them legally in English is its own adventure, mostly on niche digital storefronts or through fan translation circles, which adds another layer of friction to the discovery process. But when you find a good one, it feels like uncovering a secret.