What is the best acoustic guitar for a beginner?

I've wanted to learn to play guitar for awhile. I used to have a childs guitar but I never got the chance to learn on it, I was too busy and had a low attention span. But now that I'm older, I wanna learn. But I need a guitar, since my tiny one is way too small for me now (and I lost it). What's the best and least expensive guitar, for a good quality, for a beginner player? Oh, and where can I get one? Online or in a store.