I use a Danforth type anchor on my boat (18 foot RIB, 8 lb anchor.) As I recall, you need a relatively heavier anchor with the claw type anchors (Bruce, Lewmar knockoff, Delta, etc.)
My fluke type hooks up quite well in either sand or rock. Only place it has trouble is on flat shale (but then, so would any other anchor.) Unfortunately, that substrate is what's on my favorite dive sites.
I don't anchor in grass or mud too often, so have no experience with that type off bottom.