Let’s take a moment to look at Gryffindor’s qualities:
Many of you will see Peter as a coward, as a bad friend and an altogether bad person. I see him as a good person who was misguided.
Throughout the books, I always got the impression that Peter was not as popular as the other Marauders. It seems like he was a bit of a crowd follower, and was thankful to have friends at all. However, as time passed, he became “one of the lads”. To become an animagus is complex magic, and I don’t think he would have been able to perfect it, had he not cared enough for Remus and the others. We already know that he wasn’t as talented as his friends.
However, living in the shadow of your three best friends has got to take it’s toll. Like Percy with his brothers, I imagine Peter wanted his own time to shine, and that opportunity happened to come from the wrong place (at the right time).
In a way, he was incredibly brave to betray his friends, and give up everything he knew and loved. He cut off his own finger (that’s not exactly a walk in the park), and later his hand. He’s also very loyal to himself.
Peter’s life ended when the silver hand Voldemort had given him strangled him because he stopped trying to kill Harry, after being reminded that he owed Harry his life. He went against the Dark Lord to repay his debt. If that’s not self-sacrifice, bravery and courage, I don’t know what is.