Before answering it is good to understand what is happening when you cut with the different types of blade so imagine cutting a slice of bread with a double-edged knife, for the slice to be parallel different things happen either side of the blade. The slice effectively moves away half a blade thickness as the blade cuts and on the loaf side the bread is pushed over or compressed by half a blade thickness so the blade can take a straight path and the slice cut parallel.
Now, if the bread was stale and hard it would be more difficult to cut a parallel slice as on the loaf side it would resist being compressed and therefore try to push the blade over half a blade thickness and start it on its way to produce a tapered slice. So to prevent this using a single (chisel) edged blade with the flat side on the loaf side (rather than the slice side) it does not require the loaf to compress at all but it will push the slice away by the full thickness of the blade, which is no problem, and therefore cut parallel.
So, tough/hard boards need a single edge blade – but a double edge blade can be used on soft boards (works out cheaper because you can use both tips of the blade).
White core or general acid free boards are mid-range on the hard-to-cut scale so carry out some cutting trials using both types of blade and see what gives you the best result.