Animal abuse. Human abuse comes a distant second. I believe people, no matter their condition, have the means to help themselves in most cases. We're humans, who created a human society in which humans can thrive; the people who need help have options readily available for them, be it loving family, fiends, charity groups, social welfare programs, etc.
Animals, however, have almost no options in our society. They're sold and traded like merchandise, involuntarily forced to breed, genetically altered, crammed in to tight living spaces, mass slaughtered for food, "thrown away" if they don't serve a purpose and put "to sleep" if they need costly medical treatment. They make a crippled, mentally handicapped child appear as well-off as Donald Trump by comparison.