Maybe iZombie. Stranger Things is an ambitious, self-aware, quirky genre show. Though the comparison probably ends there. Thematically Orphan Black is close, though beyond Maslany's performance that show hasn't had a ton to offer after season one.
I'd go with Grimm. I feel like they worked the concept of so-called monsters and the adaptation of fairytale myths into real world allegories at least as well as Buffy every did; and perhaps a little better in the regard that Grimm launched the narrative from the perspective that not all wessen/demons are inherently bad, and its their actions that define them. Some are good, some really blur the lines.
They haven't really had major big bads the way Buffy did, so in that respect the narrative has been meandering, but still largely entertaining. I think the important thing to remember is that Buffy wasn't always quintessential Buffy. The measuring stick by which people tend to compare other shows to, can generally be summed up by seasons 2 and 3; as those the seasons where BtVS was at its peak. While the other seasons may offer something that sets itself apart from other shows it may be compared to, there's not as great of consensus about the virtues of a significant portion of the series.
I watched the first season of The Strain. I might watch some more eventually. But it didn't remind me of 'Buffy' in any way. I do agree that Once Upon A Time isn't anything like Buffy aside from being a female led genre show.