the fifth edition of Heavy Weather Sailing (Adlard Coles / Peter Bruce) includes a chapter on drag devices. It documents some trials undertaken between 1996 & 1998. It is pretty comprehensive utilising four different yachts and covered parachute sea anchors, series drogue, galerider, an old car tyre, a sail, etc, etc.
Unfortunately the conclusion was...it depends. No one device was best, it really depends on the circumstances, how severe the weather is, how much drag you want, etc. They did suggest that in really bad conditions (plus force 10?) facing bow into the seas maybe better (either hove too, under power or lying to a sea anchor) to avoid pooping, becoming unsteerable or pitchpoling.
Worth a read if you are interested in the subject.