Here is a quick comparison chart for the most common VLF waterproof detectors (not including PI detectors in this) that are currently being manufactured or on the way. Updated 10/1/2018. Click for larger version. Follow up posts in this thread have the details on each model.
Waterproof VLF metal detector comparison chart - updated 10/1/2018
Waterproof Pulse Induction (PI) Metal Detectors Compared