I guess for me it depends on whether the difficulty relates to experience in honing, or the metallurgical properties, hardness, etc. of different alloys. For a new honer, stainless might present greater difficulty, but being new to honing, any metal is usually difficult.
As to the hardness of the alloy, it may take more strokes to achieve the desired edge, but I don't equate that as difficult. I think the experienced honer will know the metal they're honing and make the required adjustments.
I voted #3. The disernable difference, IMHO, is the skill of the honer in recognizing the steel and applying the requisite techniques required.