Perhaps I misunderstood your original post, in that I presumed you were asking these questions because you wanted to make knives, when instead you were asking them from the perspective as an end user? In which case, I think the question you should be asking is not what's popular, but rather what's the best knife for your personal needs and tasks? It's about the right tool for a particular application first, and what's appealing to you aesthetically second. Knives are a very personal thing. The same can be said regarding steel selection, or non-ferrous alternative blade materials if you want to go down that road. I can tell you why I use the materials that I do and why I like them, but again, that's going to be vary from maker to maker.
