I loved reading as a child, and still love it today. I had so many favorite books. But if I had to choose just one book series, it would be (hands-down) the Babysitter Club books. I owned so many of these books and borrowed the others from the library over and over and over.
I still remember the first one I read. It was called Kristy's Big Day. I borrowed it from my best friend at the time, Rachel. It was the 6th book in the series. Kristy, the president of the Babysitters Club, is in her mom's wedding. The book follows her moving into her stepfather's house and the preparations for the big day.
I think it was partly due to that being the first one in the series I read that Kristy was always my favorite character. She was outspoken and a little bossy. I was way more like her best friend Mary Anne at the time, but I think that's why I liked Kristy - she had leadership skills and strength that I admired.
I think the series finally ended somewhere around 150 books. I stopped reading somewhere around 100. No particular reason, I just outgrew them.
I tried re-reading one of them recently, and to say it wasn't the same is an understatement! I do still have a number of them in my basement that I'm hoping my kids will want to read one day!