That’s a tough one, because I like so many.
For strictly looks, I’d have to say titanium with any number of inlays. The bigger the inlay the better. Of those, heavily grained oak over Ti is probably my favorite, but I also like inlays of pretty much any wood grain, cf, G10, micarta, timascus or nice swirly resin.
For functionality (i.e., comfort and grip), i probably have more smooth/lightly textured G10 than anything else. My favorite knife of all is still the Buck Sprint Ops Pro in blue/black G10. But I must confess I am starting to warm up to micarta, as long as the texture isn’t too coarse. It’s gotta have grip, but not so much that it chews up the pants pockets.