Ideally, you'd have a bit of both. A large open space is needed for a lot of sports and hobbies. In cities I see a lot more parks that are nothing more than a bit of run down looking playground equipment and a couple benches than large open fields.

The parks with more amenities tend to have things like fenced off areas, nets and marked courts for ball sports, bright overhead lights, buildings, and actual parking lots. Busy outdoor entertainment centers are nice, but open green space is important too.