Man, it's honestly Ron and Draco who end up at the center of those stories way more than anyone else. Sure, Harry gets his share, but the fics that build a whole stable of love interests around a male character? Ron's the go-to for that wish-fulfillment 'normal guy becomes super desirable' trope. It's like authors take his canon insecurities and just flip them completely, having a bunch of witches suddenly find his 'loyal, down-to-earth' thing irresistible. You see him paired with Hermione, Luna, maybe a Slytherin like Daphne Greengrass, and sometimes even Ginny in a weird twist.
Draco's popularity is more about the redemption arc fantasy. The harem becomes a symbol of his reform—he's so changed and powerful that witches from all houses, even former enemies, flock to him. It often involves a lot of pure-blood politics, with Daphne, Pansy, Tracey Davis, and then Hermione or Luna thrown in to show how he's transcended his old prejudices. Honestly, it gets repetitive. I'll click on a fic summary thinking it's a normal pairing, and bam, it's another 'Lord Draco Black' with five wives by chapter three.
The one I rarely see done this way is Neville, which is a shame. He's got that late-bloomer, quiet strength thing that could actually work for a more grounded, slow-build version of the trope. But I guess that doesn't fit the power fantasy mold as neatly.