I'm far from any expert in this hobby, but I have had some wonderful success in baseball fields, as well as schools. Although I always check around benches and such, I have actually had my best luck out in the middle of the outfield, or on any access roads that lead into or out of fields.
Hope this helps you!
Just remember... be respectful of the land... fill your holes... Try to leave no evidence that you were there!
Happy hunting and good luck!