Cairns Local here.
No there are a hell of a lot of day trippers or overnight operators to answer your question.
Don't know what your after for top of the line but descriptions of operators I have dived on.
Tusa T6 & Divers Den. 2 dive sites, up to 3 dives in total. Dive time 45 mins per dive. Can go unguided if you choose to. Roving permits so can go to many different reefs depending on the weather. Both pretty good operators.
Passions of Paradise. 2 dive sites, up to 2 dives in total. Dive time 60 mins per dive. Can go unguided if you choose to.T Pretty good set up and is becoming a lot of locals operator of choice.
That's about it for the unguided option as far as I know.
Generally most operators are pretty good I can't think of any I would not recommend.
Generally look out if you get 3 dives in and which reefs you would go to. Weather dependant as always.
Flynn, Milln are pretty good reefs to get out too.
Most Operators generally do Norman, Saxon & Hastings.
There are a few good live aboard options a Ocean quest for divers den is a good option where you can put a few days out and get in 5 dives a day.
If you can justify the time and money would highly recommend Spirit of Freedom or Mike Ball.
The outer reefs are spectacular.
There is an option of doing the outer reef with Rumrunner which is a really budget option and not as well set up or as polished as other operators but for the price is good and the diving is great.
Not to be discounted are the pontoons for Reef Magic and Great Adventures.
Have been diving them lately and the coral and life out there is really good.
Port Douglas would be Divers Den or Calypso.
But if your near Townsville or Whitsundays try to do the Yongala.
One of the best dive sites you could possibly go to.
PM me if you have any questions about certain operators.
I know I haven't narrowed it down for you but there are a lot of options.