Titanium knives became trendy ten or fifteen years ago. Titanium is not great for knives. For a dive knife, or any salt water knife, it will be hard to beat 440C. A dive knife is usually a prybar and a tank knocker more than anything else. I stopped carrying a knife after 300 or so dives because I had never once used it and no matter how I tried to tie it onto my gear it was always in the way and getting snagged. LOL, when I first started diving I had the big dive knife strapped to my calf like I had seen in all of the stupid movies from the 1970s. That was the worst idea ever, just like all of the other stupid Hollywood stuff.
A professional salvage diver needs a knife. Cave, technical, and wreck divers need a knife. Everyone else is better off without one because as a recreational diver you ought not be putting yourself into any situation that would get you tangled up. But if you still want a knife, go with a 440C blade and a rubber handle. I keep a knife in my gear bag, because you always need a knife for repairs and stuff. But it stays in the boat or on the beach where it's useful.