Who does better at detecting mouth lesions--patient, hygienist, dentist, doctor?

All of the above: Some patients are very oral health oriented and immediately seek an appointment for anything that appears in their mouth they have not seen before. For many offices, the dental hygienist is the first clinical contact for the patient and a hygienist with an excellent clinical training will often be the first to diagnose an oral lesion and consult with the dentist/doctor.

Whoever has the will: An effective oral examination is not beyond the abilities of any professional with proper training and the will to put in the necessary effort. But because oral diagnosis falls most precisely within the scope of a dentist's expertise, a dentist is likely to be the most effective oral diagnostician.