Great poll Reeti!
Mine's was a close tie between Hedwig and Crookshanks, but I finally went with Hedwig, because she had always always been there for Harry as the only living being at #4 Privet Drive who wouldn't flinch when looking at him. It was almost as if she knew what he was going through, and I was really very sad when she died in the beginning of Deathly Hallows.π
But I love Crookshanks a lot too, because if it hadn't been for him (or herπ³; don't remember its gender), the trio wouldn't have been able to meet Sirius in Prisoner of Azkaban, and find out the truth about Harry's parents' deaths.