Welcome to OCF. The best places to get treated are at top rated comprehensive cancer centers (CCC). There will be a team of specialists who are familiar with treating many cases per year instead of a small facility where they may only see one or 2 oral cancer patients a year. A large facility will have more experience and resources available to the patient.
I would suggest he goes to a CCC for a second opinion. As you wrote, each specialist will recommend their specialty as the best way to treat him. This is just another reason for a CCC, a whole team will meet and discuss the patient and decide whats the best way to cure them.
Here is a list of CCCs and also the NCCN treatment protocols.
NCI CCC list NCCN Guidelines