Jack's is still there - on Alii Dr. in south Kona. The boats all leave from Honokohau harbor north of the airport. Most of the operators keep their boats there - usually you check in at their shop/office in town then meet at the boat for diving.
We like Kona Diving Company. Nice People, smaller outfit. Big Island Divers also does their:
Long Range Charter | Big Island Divers Monday and Thursday.
All the south Maui boats leave from the KIhei Boat Ramp - Wailea being just a couple miles farther south if that's a factor in your resort selection. I don't have a particular preference among Ed Robinson's, Mike Severns Diving or B&B Scuba - all well liked/regarded here. There's also other good operations in the area - just 3 I have some personal knowledge/exp. with. Robinson's offers some "Adventure" trips also - 2-3 tank trips certain days of the week.
In Lahaina I
think you've only got three choices now - a couple of the other dive shops in the area book on local boats.
Lahaina Divers has the 45' Newton diveboats, they send one to Molokini Crater every other day so it's possible to dive Lana'i one day and Molokini the next. Besides the regular dive sites - often one of the Cathedrals - they also do their West Maui Drift dives - considered more advanced. I dove that once - it's a ride..
They also go out to Molokai once a week to dive with Hammerheads but IIRC there's a season for that - IDK when.so check with them. Lahaina has 2 big boats and often fill them. But they segregate by level and provide a DM for each group of 8. I have been out to Sharkfin once on their boat with 6 others but it was a fluke - a big group canceled earlier in the week.
Extended Horizons has one smaller boat - only to Lana'i. Don't know much about them. Lastly there's Hawaiian Rafting Adventures with a big fixed hull Zodiac. It's fast but when we saw them at the Cathedrals once they were getting tossed around pretty good on the mooring.
There's also guided shore diving on Maui/. Some of those options are Shaka Divers or Maui Dreams Dive Co. in the Kihei area, In/near Lahaina there's Scuba Mike, Tiny Bubbles and one I forget. Plus I don't know all those operators either.
You're smart to stay near where you plan to dive. I really like Kapalua north of Lahaina but it's not cheap. You can access everything in Kahana nearby - including a Maui Dive Shop for shore tank rentals, the Ka'anpali resort area then down into Lahaina with all it's shops etc. Ka'anapali is the area with the big high-rise condo complexes - not my style. There's even traffic congestion in the area at times.
I've never stayed in Kihei but the north side seems to be a lot less commercial. There's a boatload of condos around town and south so you can find some good deals across the main street from the beach. (Kamaole 1 & 2) They're dives but there's people on the beach/in the water usually.
We like Wailea also - there's some big resorts there but you'd never know it due to their being situated on the various beaches/bays. And lots of low-rise condos between them. Most of the better shore dives are in Wailea - not Kihei.
