Spontaneously, I would say skim coat, but it depends on the conditions as usual. Calculate the material consumption and cost. Regular wall filler can't be applied too thick, so if there are large holes, you might need to fill with, for example, gypsum plaster which can be built up thicker. Plastering with sheets often uses up an unnecessary amount of material, which is relatively heavy to transport and partially an unnecessary cost.
It takes a few days to learn how to skim coat with decent speed and surface smoothness, but it pays off once you've learned the technique.
A thin layer of plaster followed by regular filler, I have found to be most effective and economical. Then again, it partly depends on the surface; if it's a wall with large cracks, it will likely crack again, in which case plaster might have been better.
I am planning to drywall the ceiling with sparse paneling to maximize the height as much as possible, but I have heard that you can't drywall with sparse paneling, is that true?
