Human Rights Watch has released its 2015 World Report, a 650 page document that goes through the human rights records of every country.
Here is a chart for how often some nations are named in the report:
This gives you an idea of how skewed HRW is when dealing with Israel, placing its importance as a human rights violator somewhere between Syria and Russia.
This isn't a perfect metric. For example, I didn't include the United States (83) because many of its mentions have nothing to do with human rights. "Palestine" or "Palestinians" are mentioned 98 times, but the vast majority of those mentions were regarding them as victims of human rights violations, not violators.
Even with those flaws, this chart is a fairly accurate view of HRW's thinking on who are the biggest violators of human rights, and therefore it is a good indicator of HRW's anti-Israel bias. To think that Israel's human rights posture is deserving of more attention than those of, say, the DRC or Saudi Arabia or Mexico is the height of absurdity. However, it fits in very well with the patterns we have seen in HRW reports and Ken Roth's tweets being heavily weighted to damn Israel far out of proportion to any human rights issues it has..