Now, i have to admit i 愛 both series! I'd say harry potter is unisex and appropriate for all ages, whilst twilight adresses mainly to teenage girls. HP talks about friendship and love, while twilight is もっと見る romantic! Also, hp gives lessons of life, although maybe in some cases, i would prefer 読書 twilight.
Finally, They are both written によって two very talented and imaginative writers, j.k rowling and stephenie meyer. They wrote these 本 to give teens (and not only) inspiration and time of happiness. So, if あなた don't like one of these two series, don't blame them! We can't all have the same tastes!