I am no expert in cruise ship diving from Phuket. But let me tell you Phuket is one of the worst places on earth to dive. The sites and the dives are nothing to write home about, and the sheer logistics of diving from Phuket are just ... the worst. Im going to get some flack from local operators, but truth be told, this is the way it is. Dive sites are far. And I mean, FAR. Mainly close to Koh Phi Phi. You end up crammed in a very BIG boat; think more than 50 divers. Out of those 50, half are brand new divers, a quarter are new divers, and what's left is probably going to be nothing to write home about in terms of diving experience. Dive times are severely shortened, because the big boat operator (not so much the individual guides you might get with whatever dive shop you choose) wants to run a schedule (of more than 50 divers, so 40 minutes is 40 minutes dive time). Again, no operators really manage their own boat (ScubaCat does I believe, but then again, it aint no fast machine either). They will all sublet space on one of the big boats. So your dive shop "experience" will only be regarding your particular guide/instructor that dives with you. But they have no say on the dive site, or the times, or any other stuff.
Really, diving in Phuket for an experienced diver is a waste of money and time. That's what I think.