I don't know much about Honolulu (I tend to stick to Maui and the Big Island) but I can tell you that Hawaii diving is great, and while the summer can be a bit warm, I can't think of many other placed I'd want to be. Nice structure, interesting life, lots to see and a wide range of diving options both on and off the shore.
While it's not strictly a diving perk, one of the real advantages to Hawaii that keeps me going back is the variety of other things to do. There are a lot of great tropical places to go and dive, but many aren't good for much else. Hawaii doesn't have that problem and unless you plan to live in the water (which is a viable option), there's a nice amount of diversity in activities.