My first manga was Absolute Boyfriend. and It's still my favorite. I actually read it in the bookstore. XD
When I was little my mom worked at the mall, so I would go in with her on the days she worked,
and I would go to the bookstore & sit and read...not buying anything. :P
It's so hard to remember which was the first manga I read. I think it was possibly Shugo Chara, or Fruit Baskets.
I've read so many over the years now.
When I was in junior high my friends were completely obsessed with Sailor Moon, so I got sucked in. One day my friend brought Japanese volume of the manga to school and let me look at it. I didn't understand the appeal at all, since neither of us knew enough Japanese to read it. It was while I was browsing at the bookstore that I got interested. My first series read and purchased was Marmalade Boy.