Physiotherapy, Motivation, Man-Management, Discipline, Determination, and Fitness are the key attributes for a good Physio, also factor in Working with youngsters which is important if you have a young squad or good youth development.
If you can find a Physio with high ratings in all the above he will be (or will become) World Class!
I try to find at least one with high ratings in all the key attributes and then have at least two more (at bigger clubs) to reduce the workload... the better your number 1 Physio is, the quicker players will return from injury.