Database design: Which will perform better, auto incremented column or a composite key for appointments The schema of table is :

appointment(date,time,patientID,...)
pateint(patientID,PName,age,...)


PS: two or more patient can came at the same time .
    The number of appointments per day up to 500 .

Which is better for performance, using auto-incremented primary key or a composite primary key (date,time,pateintID)?
From a purely performance standpoint, using the identity key as a clustered primary key will be most efficient. From there I would do a non clustered key with a unique constraint on datetime, patientid.