We've been diving with Ed Robinson's for 10 years and will keep diving with them as long as they're in business.
However, Dive & Sea, Makena Coast Charters, ProDivers, Mike Severns, and B&B are all excellent for S. Maui boat diving. For S. Maui shore diving, Shaka Doug and Maui Dreams can't be beat.
For Lanai, Extended Horizons and Lahaina Divers are your two main choices. We go with Lahaina Divers because the crossing can be rough on the way home and we like the bit 46' Newton dive boats for a better ride. The trade off is that the diving is an "underwater tour" and you only get Al72 tanks. For us an Al72 will last over an hour and we have no problem being the last back on the boat, so we push Lahaina Divers' limits. Extended Horizons uses AL80s and doesn't have as short of dive times.
And of course for scooter diving, our own Greg Walker (Maui Scooter Divers) is reported to be the best...and I believe the reports! One of these days I'll get out there with him.