Their all pretty much standard wheels you would find in any shop, I've used them all..
The blue will be your standard middle of the road grinding wheel for general work, the white is going to be a softer wheel and will run cooler but break down easier than the blue.
What you want to pay attention to is the grit and the wheel composition. There will be a code on the label, Im betting the blue is somewhere around a 46 in a vitrified bond denoted with a V. The white wheels are likely a more open bond .
This guy does a decent job of breaking things down.