I have been to Patong on Phuket twice now and use Scuba Cat, look at
Scuba Diving - Liveaboards - Padi IDC – Tec Diving - Phuket – Thailand - Scuba Cat Diving for all my diving. Their livaboards are good and not expensive. Had a great 3 day livaboard to Min Huang & Min Duang a few years ago, saw 10 Manta Rays, the business. Have a look around the very large site for more info.
Hope it helps?