Assuming both categories got the same attributes,
there is no difference in query performance (According to Multiple Table Select vs. JOIN (performance) )
In that case the solution with one table uses slightly more storage than the two table solution as you need a further column for differentiation (e.g. type).
EDIT
As your structure is different, you should use the two-table-solution as you get NULL fields if you use the one-table-solution.
A bad example for the table Publications:

In the given example you do not need an additional attribute to differentiate the two types because you could determine the type by Pages or Director.
You should avoid NULL values, especially when they are not meant to be filled with data in the future.