Most likely something simple - anything from 1050 to 1075, 1084, 5160, 15N20, or whatever else was available. Their decision would primarily be driven by price and availability, so long as performance was decent. I'd imagine they'd view the steel and the weapons produced from them as tools, and spend more time thinking about how they could use them than worrying about what kind of super steel they might be missing out on.
That said, I'd guess the rich and elite would use something like 3V/4V, Z-Tuff, damascus/pattern welded, or any kind of fancy stainless. I'd expect high-toughness steels would be preferred, as relatively brittle steels with high wear resistance are better for smaller knives rather than large chopping weapons / tools. M390, Elmax, S35VN, and any other "super steel" from the modern world would largely be limited to small, personal knives much the same way they are in the real world.