Probably the united states. They've killed millions of people around the world in the last decade. If you don't limit it to the last decade, it's even worse.
Yeah. It's not the crispest distinction to make. But, note that the U.S. has also helped a whole lot of people.
a - b = c
Being utilitarian about it, which country has done better in the last decade?
Being utilitarian about it, India or China is ahead no matter what, because of all of those little sacks of utility known as "babies" they've produced. ;)