I’m a traditionalist or purist when it comes to this argument, but you’ll hear people argue both ways.
I feel that when you use a relative pronoun with people, it should be who or whom. Others feel that the universal that is perfectly okay. In fact, most people use that when speaking and writing. I use it in speech, but try to replace that with who or whom when writing.
Here’s what I’m referring to:
It was John who got the job.
It was John that got the job.
The second usage sounds ugly to me. Of course, in this sentence we could solve the problem by simply saying, “John got the job.” However, I still maintain that people deserve/demand who while animals and everything else call for that.