Who is the best person to diagnose and treat TMJ : ent, TMJ dentist, oral and maxiofacial surgeon or cranial osteopath?

Depends on the cause. Usually the first person to discuss your symptoms and details with is your dentist. After helping to discern what the root cause of the issue is, then they can help make the appropriate referral (if needed) to someone that can best assist your issue.
TMJ. It depends how severe it is. For mild (internal derangement) a splint might be helpful and can be made by any dentist who has knowledge of tmj. For more severe cases (degenerative) you need to see an oral surgeon who focuses on TMJ surgeries. Usually ENT doctors do not treat tmj. In any case, first thing you need is a good panorex and maybe MRI if there is a disc issue.
Varies. Varies with the communite. Any dentist can be a TMJ expert with the proper training and experience. Most commonly, oral surgeons, prosthodontists, and orofacial pain specialists. Ask your MD, your dentist and your dental society for referrals.
TMJ specialist. You can go to website, www.Aacfp.Org which is the american academy of craniofacial pain. There you can finds many dentists who are trained beyond general dentistry in diagnosing and treating tmj/tmd.
Trained dentist. Although it is not a specialty recognized by the ada, there are dentists who focus their practice on the diagnosis and treatment of tmd. They usually have a wide range of diagnostic skills and can offer multiple treatment options depending upon the diagnosis. For a list of dentists see www.Aacfp.Org and www.Aaop.Org. Treatment rarely involves surgery or complex dentistry.
Experienced dentist. To determine what issues are causing the symptoms and explore conservative treatment, i'd suggest the dentist as the first stop. The other providers you mention are focused on specific treatment modalities that may or may not be relevant. There are exceptions to this generality and some surgeons are very good about exhausting non-surgical solutions first. There are many philosophies about tmd.
TMJ dentist. I personally feel that a TMJ dentist is the best avenue. Particularly if they are trudenta trained as this seems to be the most effective at relieving the symptoms by addressing the true causes.