Very very first ever read with my own eyes? I don't remember for sure, but the candidates are Happy Hollisters, Bobbsey Twins, or Nancy Drew.

First adult series I read (when I was well before adult!) was the Mrs. Pollifax books, I think.

Very first read to me was Chronicles of Narnia, my mother's pick for reading nights.

Very first to own was my mother's old Nancy Drew books, back when Nancy was a blonde and drove a roadster.