Locator Attachments or Mandibular Overdentures?

Authors

David, a dentist, asks:

What is the current thinking about using Locator attachments for mandibular overdentures?
I would like to know which design works better in the mandible, two or four dental implants with Locator attachments? Are there any better attachments that are being widely used? What about using dental implants and overdentures in the maxilla?