I agree with Khairil- you can still find nice places on Tioman. Just check it here: http://www.mytioman.com/opencms/opencms ... ml?lang=en
(this website seems to have problems, sorry)
Tioman has much more cheap accomodations than Redang and Tenggah, but also high quality resorts.
It's also great for diving, many different spots, but mainly according to the small islands around Tioman. Snorkelling like on Tenggah and Redang (just go to the beach, jump in the water and enjoy the healthy corals) is also possible in Tioman, but you might be dissappointed: only few fishes and many corals are dead close to the beach. Better to make a snorkelling-trip by boat- to coral island for example.
I say the islands in Terengganu are still much nicer (even the business is growing too fast), but Tioman is a trip worth if you are a scubadiving-junky or if Terengganu is too far for a trip.