Well that is obviously a matter of opinion.
I guess the simplest answer is one that gets results, one that makes their clients better.
The therapist needs to firstly have a good understanding of anatomy and physiology so as to understand where the imbalances in muscle tension lie, where they come from and how things interrelate. They need to be able to see the bigger picture.
However, probably equally important is a good sense of touch. Not all therapists have this it is not something that is assessed in exams. A therapist with a good sense of touch will will find the right spots, even if you didn't realise that was the spot. They will most of the time know just how firmly to apply pressure and they understand that it is painful at times and very uncomfortable at others.
A good therapist will also treat the cause not just the symptoms.
So an example is probably appropriate here.
New client yesterday. They had seen a couple of other professionals re their injury. The client reported pain in an adductor muscle along with some knee pain which has been diagnosed as arthritis. Simple visual assessment told me that the client had tight lateral rotator muscles of the hip. That the right knee was in line with the foot but that the left wasn't and that this was a key factor in their problem. There was also a visual imbalance in the quadriceps, all of which tied in with the clients sporting history. The plan massage to resolve the current pain and loosen the muscles that are tight. Advice on stretching to help prevent tightness coming back and on exercises to build strength in muscles that are weak. The work to completely correct the imbalances will take a bit of time but if we can together work with a plan to resolve the issues then the adductor pain should be resolved and the knee pain reduced.