Every knife in my collection is "the one." I see a knife and decide it is a perfect fit for me. It is the knife best suited for my life and my tastes. I carry it and enjoy it, but I keep looking at other knives like an idiot. So, naturally, I find "the one" again.
I tend towards, the perfect middle of the road knives. Ones that are not limiting. I want them strong, but light. Durable enough I don't have to worry about it, but thin enough to slice. Big enough for food prep, but small enough to use in public without making a scene. Well made, but not too fancy looking or so expensive I can't justify using it. My favorite knives are my L and S Sebenzas, delica, mini commander, 0566, and skyline.