Around 2007, I spent time in Davao and went diving as much as possible. I really enjoyed the stay, mostly because of friends made through the dive shop. The night life was decent, some good spots can be found with local knowledge. My memory is not good enough to make recomendations, and perhaps 15 years is long enough that my info is outdated regardless.
Keeping in mind that things may have changed since my stay, here are a few thoughts about diving.
The Davao diving scene is locals oriented, which was a nice change from the more touristy spots. Same for GenSan which was another of my favorite spots off the beaten path.
It is easy to get on a boat for weekend dives, but weekdays are generally not dive days. Most likely if staying in Davao City, diving every day will not be possible unless your pockets allow for financing special trips.
Some resorts and spots on Samal Island are good for shore dives during weekdays. Staying at one of the many resorts on Samal vs in Davao City itself would be an option to consider if diving is top priority, but then Davao night life is not as easy to get to.
The most regular dive spot was Talikud island, with an offering of decent/average dive spots and very nice location for surface intervals.
The best boat dive spots were on the East & North/East side of Samal, but these were not often available due to the travel distance, weather, etc. Boat rides tend to be fairly long, but the scenery is good and the boat ride back to the dock at the end of the day is made even better with a cooler full of San Miguel.
Overall the diving in Davao was average compared to other popular spots in the Philippines, and the challenge of making dives during weekdays should be considered. There were some sites pretty much dead from cyanide and dynamite fishing, so dive site quality ranged from poor to very good. It was worth it to me since I had time to spare and enjoying most any kind of diving. It might be a disapointment for a seasoned tropical diver staying a week or two, unless you get a ride to the nicest sites on the weekends.
If you haven't already, take a look at GenSan as another possibilty.