Sirius Black
"I told Albus," McGonagall said over her tea cup. "The worst sort, those Dursleys. But Albus was certain they were family and would love him. And..." McGonagall paused. "I couldn't just leave the child alone like that among strangers, you know, so I popped in and checked on them. From what I've seen, they keep Harry with their own son and seem to be treating him fairly."
"Petunia hates magic!" Sirius pointed out. "She was rude to Lily when she went to her wedding and sent nasty letters when Lily tried to invite her to her wedding reception. I don't see it."
"Petunia Dursely does not hate magic." McGonagall said. The few days she had observed the Dursleys with Harry in their custody had made that clear. "She hates not fitting in, she hates the fact that magic took her sister away from her, she hates not being invited to her sisters' wedding because of a 'freak war', she hates that magic was responsible for her sister dying and leaving her child an orphan. All of which are very valid facts. But," McGonagall paused. "She does seem to care for her sister's son. Wants to do right by him. She doesn't want to lose him like she lost her sister."
"All of which means, Harry is safe with them," Remus explained gently.
"I don't know, Moony," Sirius frowned. "There's something wrong, I'm sure of it. I feel it. I just can't explain it."
"There's also the matter of the blood wards," McGonagall said. Sirius and Remus stared at her in confusion. McGonagall explained, "Lily's sacrifice formed a blood ward around Harry, protecting him from Voldemort and all sworn to him. The upkeep requires Harry to live with Lily's relatives at a place that is a 'home'. Harry is, magically speaking, safest at Petunia Durselys' home. Think of all the Death Eaters still free, Sirius. What if they went after Harry?"
"Fine," Sirius scowled. "Fine. But I will be observing them too. If those Dursleys harm one hair on Harry's head. Just one-!"
"If they do that, I will personally help bring Harry back to you." McGonagall assured him. Sirius nodded and gave in.
The moment any of those Durselys hurt his godson, all bets were off.