I have two favorites ,just because it's hard for me to pick an all time favorite between so many genres, Inuyasha and Something About Us.
Inuyasha is just a classic action series. It's got everything I look for in a manga, drama, great fight scenes, an interesting plot and some romance.
Something About Us is my all time favorite romance series. It's a series that every fan of the romance genre should check out, and it perfectly captures the feelings of going from being friends with someone to falling in love with them. It also has one of the best plots that I've seen in a romance series.