Steffen Seasports is not bad. I just (2 weeks ago) did some dives with Turtle Bay Divers. Both are not bad.
Tokong Laut is good. I saw my first big Seahorses diving the Vietnamese Wreck (not much left) with Seahorse Drift.
On P. Kecil Coral Bay is quieter, not so hot and more cozy, while Long Beach is more happening.
My suggestion is stay on Coral Bay (Maia Chalet for something simple, else try Senja; The name of the new one is Shari-La, just at the Jetty, but there's some construction going on so make sure what room you get and it's to sterile for me, no character) and go over to Long Beach (5-10 min walk) for party and the nicer beach now and then.
Just call Ricky (from Steffens), or look for Shikin (a travel agent) at the Jetty, she normaly knows what offers there are. She also should be able to sell you a boat ticket.
There's a group of huge Bumpheads just behind the jetty on Long Beach. And from Coral Bay cross over to the "Secret Beach", we saw Octopus and Cuttlefish there snorkeling. Three years ago I saw two Black-Tips there, too.
If you have a lot of time (and don't mind the money) make a day trip to Redang, the visibility there is better.
And try the shakes. My favourite is the Snickers-Shake, with a close second Mango-Shake. Power!
And the BBQ at night (try the one at Coral Bay). Banana Pancakes for breakfast!
One last note: Make sure to actually call the Jetty or tell your Resort to book a place on the boat for the day you want to leave. If not there are not enough boats and either they are dangerously overcrowded or some have to stay on the island...
