Ke'e Beach offers great beginner and intermediate snorkeling. It will help if you have a tide chart. Their are numerous turtles there but you usually must go over the reef to the drop off to see them. The reef is very shallow at low tide and not very passable. You should not walk or crawl on the reef. I am about 220 lbs. so I have to wait until high water, but my wife who is considerably smaller gets out easier than I do. There is some current at the drop off but in all of the times we have been there it is not really threatening. We have never failed to see turtles there.
Tunnels Beach has a little more variety of fish and you can get to deeper water easy. It also has more coral formations than Ke'e.
We have taken the Napali Coast snorkel boat a few times and the scenery is amazing if you have not done that. We encountered numerous spinner dolphins along the way also. The snorkeling at Nuololo is average but we did have our first shark sighting there. Very exciting as he came around a couple of times and just passed below us and was off. It was a white tip reef shark which are normally very docile but we did attempt to keep our distance.