I understand the diving generally gets better as you move north among the islands, so Kauai should be quite good.
The latitude has little to do with the diving, so the two ends of the above statement are not related. As mentioned by Friscuba, soil (sand) and run-off (rain) can have a large impact on dive conditions. Kauaii is the oldest of the Main Hawaiian Islands, with very likely the highest percentage of soil. It is also evidently the optimum height for producing rain from our trade winds (one of the worlds wettest spots).
In general the visibility is better as you move South East (younger islands - less soil - less rain). There are notable exceptions to that rule; Ni'ihau is a small rocky island off Kauai with arguably the best diving in the Islands (summer only), West Oahu is pretty darn dry normally and the Mahi Wreck / Makaha Caverns boat trips are very popular and of course there is rarely less than 100' vis at Molokini off South Maui. In general, the Big Island (Kona) has the best vis, and is home to the only viable live-aboard.
Both Kauai and Oahu have epic cavern diving
in the summer (Tunnels and Pupukea), with Kauai's turtles possibly being largest due to more limu and algae to eat. Oahu has the best wreck diving, Maui might have the best over-all shore diving and Hawaii has the best Manta Ray diving (night). Lanai has a couple of the most mentioned dive sites (Cathedrals I & II) but most divers go with a Lahaina charter, not from Lanai.
My wish list for major Hawaii dives I have not done is; Ni'ihau (Kauai, 3-tank boat), Moku Ho'oniki (Molokai, 3-tank boat), North Shore Explorers (Maui, 2-tank RIB), Au'au Crater (Kona, 3-tank boat) and the Maui Ocean Center aquarium dive (arranged in descending price). Dives I will never tire of; Pupukea (Sharks Cove - Three Tables), Tunnels, Makena Landing (Makena Caverns!?!) and Molokini in February by kayak (on second thought, that dive does tire me)!