Tex-ArozziInput lag, but companies don't ever care to measure this. They only brag about response time, which is not only mostly irrelevant but also a wildly inaccurate way to indicate a display's responsiveness considering response time varies in different areas of the monitor (and depending on what colors you're transitioning to).
A pursuit photo and total input lag number would be insanely helpful for buyers, but there's no chance we'll ever see these advertised on products. They must be left up to professional reviewers for now.