As you can see, serials are entered under title by a process of elimination.  Title main entry is the most common choice of entry for the majority of serials.  Enter a serial under title when:

there is no responsible corporate body (excluding commercial publishers) or

the serial does not emanate from the corporate body or

the serial does not fall into one of the categories under AACR2 21.1B2 and

there is no person that is solely responsible for the entire run of the serial.

See also:

Module 4.  Main and Added Entries (Fields 100-111 and 700-711)