Having dived with several ops on GC, I now do almost all of my diving with DiveTech, and they are great. They are not what I would call a concierge dive op, but they will help in any way you need if you ask. The DMs have really helped me to improve my diving technique by volunteering suggestions. I was impressed that they were even observing me. They always seem to come up with good dive sites, and in general there really aren't any bad ones. And you'll be in north wall season, so they will probably go there conditions permitting. Regarding sting ray city, personally I'm not a fan. We do it if we have visitors who want to do it, but I'd rather see rays on a "real" dive rather than what feels like a circus act. I second the shore dives at Lighthouse and Macabuca/Turtle reef. And the food at Macabuca is great. It's our default place to eat out. And if you like spicy Caribbean jerk chicken, don't miss Chicken! Chicken!. And their sister restaurant Cimboco is good as well - both less expensive casual places. And the steamed island style mahi mahi at deckers is the best I've had. We've eaten at most of the more expensive places, and to be honest I think there is an inverse relationship between the amount you pay and the quality of the food (well, except for Blue). For the local flavor at lower prices, check out heritage kitchen or west bay diner, and if you make a pilgrimage to the East end, eat at Vivine's Kitchen - you order at her back door and eat in her back yard. Forget the menu and just get the fried fish of the day.
Have a great stay!