If you *do* decide to go with preschool ...
I'm a big fan of Montessori for preschool. It's much more hands on than a lot of places, and learning is encouraged -- but there is some direction, and children are taught a lot of self-help and independence skills. My ds6 attended an 5 day a week, full-time early childhood Montessori program (that's ages 3-6, including a K year), from 4y4m to 5y2m.
DS then 4, as an only child, didn't have a lot of experience doing things for himself -- I just always put on his shoes, since it was faster and I had time. I just made his lunches, since he couldn't reach the counters. Montessori gave him exposure to doing things for himself. He grew leaps and bounds in his personal abilities and confidence.
He also grew leaps while he was there academically. His math increased exponentially as he explored their manipulatives; he went from barely interested in adding to adding double-digits in his head, skip counting by random numbers (by 3s, 5s or 8s, for example), and completely understanding money and simple decimals and fractions. Not all of that was due to Montessori instruction itself; but he had an aptitude, and being exposed to the manipulatives was like a light switch in his head. They didn't do a ton for his reading, but he was self-driven there, and literacy teaching at Montessori is easy to differentiate.
If Montessori isn't an option, I'd go for play-based; ds actually went to a play-based nursery for the year before he started Montessori. It was fine; we just felt he was being understimulated there, and we were right -- he was a happier kid at Montessori.
