Most common type of oral nevi in oral cavity is:
Melanocytic nevi are classified histopathologically according to their stage of development. The junctional nevus represents an early stage, in which thèques of nevus cells are confined to the junction of the epithelium and connective tissue, especially at the tips of the rete ridges. As the nevus cells proliferate, they begin to drop off  into the underlying dermis or lamina propria. When nevus cells are present along the junctional area and within the connective tissue, the lesion is called a compound nevus. 
In later stages, the nevus cells are found only within the connective tissue. In the skin, this stage is called an intradermal nevus; the intraoral counterpart is called an intramucosal nevus. Most intraoral melanocytic nevi are classified microscopically as intramucosal nevi. However, this finding probably reflects the age (average, 35 years) at which most oral nevi undergo biopsy and  diagnosis, because these lesions would have evolved earlier through junctional and compound stages.
Reference: ORAL AND MAXILLOFACIAL PATHOLOGY, Neville, FOURTH EDITION page no 352
Intramucosal nevi
Blue nevi
Junctional nevi
Spiltz nevi