Since you are going to be in the north end, I would HIGHLY recommend doing the Mala Wharf dive. Although the legal entry is a bit of a PITA (wading through coral heads) the dive is still worthwhile. There is a resident white-tipped reef shark, and I have seen schools of snapper, turtles, and nudibranchs there. The structure makes for great swim-through opportunities. The dive is shallow and full of light. It's one of my very favorite Maui dives.
Old Airport, just north of Lahaina, is another very easy dive. It's a site commonly used for training, but you can see a fair amount of interesting stuff there.
Honolua Bay is beautiful when the water is calm. You can swim out along the wall on your left, and then come back in very shallow water over the reef top. It is a good long walk from the parking to the water, though, and don't leave anything valuable in the car.
In the south end, Ulua Beach is a very pleasant, easy dive. Get there early in the morning to get parking. The first reef is the one you can see extending from shore into the water, and then there is about a 50' gap (at 240 degrees) to the second reef. There is a turtle cleaning station there, so you often see them.
A little further south, Polo Beach was a WONDERFUL dive. The coral is in amazingly good shape, full of color and with quite a lot of life. Again, it's a good hike from the parking to the north end of the beach, which is the entry site, and there can be surf there.
Molokini is fun, if you haven't done it before. My favorite charter is Mike Severns, because Pauline, one of the owners, is the co-author of a book on marine life of the islands, and she is a very good guide. I thoroughly enjoyed the pinnacles and the Cathedrals off Lanai as well. If you use Lahaina Divers, be aware that you CAN request larger tanks (at an additional charge). They use 72s normally.
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Have a great trip! It's so much fun to dive in warm water you can see through . . .