You pose a good question and I can't say that I am in a position to really know yet. I am still largely getting a feel for styles and features that I like in my traditional knives, like blade shapes for instance. My two most carried knives out of my very modest collection are my #35 and #71, I love the spear blade on the #35 and the #71 is just a wonderful working man's knife that is unapologetically simple and somewhat drab, yet functionally is top notch.
That being said, I like the heft and feel of the 2-blade #53, yet I found that I only really use 1 blade, primarily the sheepsfoot. So I think I still prefer the single blade styles (a carryover perhaps, from my more modern carries). As a result, I am rather excited about the upcoming run of #54's and have preordered a single spear blade variant. This potentially could end up being "the one", a single blade design, spear blade which I already know I like, and it is on a larger frame like the #53. I also am excited to have the opportunity to acquire this year's forum knife. A single sheepsfoot blade TC Barlow, with micarta scales. It would potentially be my first Barlow, which is a style I have always found to be aesthetically pleasing but have never really handled, so the jury could still be out in that regards....
In terms of handle materials, I know what I find pleasing to my eye: Red bone, black woods, canvas micarta, and dark horn.
I guess in the end, I really do not know what "the one" for me really is quite yet. Hopefully I will know once I find it. In the meantime, I will continue to enjoy the ones I have and maintain the eagerness to try others in the not so distant future.