So, um...how do you get the best ending? What triggers it? I am going to replay the whole thing and I want to make sure that this time I get it right. I know it's a very spoilerific question, but I just thought I'd ask. XD
You have to get to your dog in the end. In the last section there are two branching paths. If you go left (the scary path) you can find your dog or if you go right, you should hear a whimper coming from the tunnel and then you have a last chance to save her. Sorry there's only 1 good ending and there are 3 bad.