I used Jack's Diving Locker, and although we had to cancel the Manta dive (rough seas, no Mantas) I did the Blackwater dive with them. (They call it Pelagic Magic)
What I liked about Jack's was that theirs started just after dark, versus Big Island Divers' starting after the Manta trips return, after 10 PM. For me, still jet lagged from the east coast, it was too hard to stay awake that late. Also they leave from the pier in town rather than from the marina up north near the airport, so less travel time for us.
It was an amazing experience! And only 3 of us on the boat that night!