The best preschool for your child is HOME.
Which is where they are, but I think a very limited preschool setting at age four or so is a good thing, also. I'd like to find something for a couple hours, three mornings a week or so, just to give them some fun time and to meet some other kids. I'm not looking for someone else to raise or educate my boys, just somewhere for them to play with a group of other children. Years ago, kids could do this in their neighborhoods, but not anymore (at least not where I live).