My tops have to be
2: Yamada-kun and the Seven Witches
3: My Teen Romantic Comedy SNAFU**
3: The World God Only Knows
5:When Supernatural Battles Became Commonplace
6: Saekano: How to Raise a Boring Girlfriend
7: The Monogatari series
How about you guys?
*Toradora is my favorite probably because the thing I hate most in harems is when they don't choose someone, and I love their relationship in that.
** I don't know if this is technically considered a harem, but there are at least 3 girls who are crushing on him so I'll just put it on the list. This show is good enough to be on any list, regardless of genre.