"Prone" probably isn't the correct term IMHO. It will rust, but I've had many, many knives made from white steel that NEVER rusted.
White will get sharper...but you have to have the skills and equipment to do it.
HD2 is a stain resistant steel, but it will get a slight patina over time. Nothing like white will though.
White is easier to sharpen, by a slight margin.
Those are my observations....but I've never tried both on a long term basis to get a feel for edge longevity....then again I've never really done that for any of the really good steels as I'm just a home cook that like's to sharpen so my knives never really get dull.
At the end of the day, they are both great, great steels and I doubt I'd personally buy one over the other based on the steel. I'd use some other determining factor. But, I don't mind stainless either.