United vs. British Airways to carry a dog in cargo?

Hello, I am wondering if anyone has any insight into which airline company is better as far as handling of dogs in cargo and being careful. I have to regretfully put my dog in cargo from Bangkok to Chicago and this is a long way. I have no other options at this point and I just want him to get back safely without having to worry too much. If anyone has any stories or information I would be very grateful.