I'm still on the fence about W. just because he didn't really do anything on his own, he just took the excuse to continue his daddy's war. I think if Sr. had gotten another term in office he would have ramped things up, but either way I think the family as a whole pushes up there on the list.
For the rest of the list... yeah it's not hard to find a lot of presidents who have killed a lot of people. However the original question was about the worst president overall, which to me includes the damages done here at home. Trump is high on my list simply because of how far back he has set us in terms of equal rights, moving beyond the pettiness of racism, dealing with important things like the unfolding climate disaster, and his nonchalant attitude that Palestine and Ukraine need to just surrender because being in the news cycle is inconvenient to him. Looking at Trump's agenda of just how much he wants to destroy things here, I find it concerning that the only thing stopping him is a few Republicans that still have a moral compass.