the titles explains all
I see some hard throwers land softly (Gulliermo Mota, Andrew Cashner, etc.) and some actually land hard after 'driving' their body (Lincecum, Lindstorm)
what is the more efficient way to throw?
I think soft is much more common.
I'm not sure it matters either way. However, "hard stomping" can lead to ankle and knee damage. Just look at K-Rod.