My overriding concern would be safety, which I have covered in an answer to another question. With that in mind, I would look for the widest variety of equipment that my budget could handle. I would try to choose equipment that is not only fun but also builds motor skills.
I would also try to encourage cooperation, planning, and creativity. In addition to the usual swings, slides, climbing frames, and monkey bars, I would try to add lots of loose materials that children can use to build objects of their choice. The loose items might include milk crates, tires, cardboard boxes, nets, fabric, stones, and flower pots, for example. I would also look for equipment that would be suitable for both children with physical disabilities and able-bodied ones.