My favorite good guy side character is, sorry to be oh-so-biased, Marco's dad. I reread some books from the series just to pick someone else. Alas, it did not happen.
Here are the whys:
1. The way he accepted the Animorphs and Chee situation was commendable. It didn't take time for him to swallow those facts - that's when I started to like him.
2. He rhymes in conversations with Marco. How cool is that.
3. He's a skilled engineer; he's so skilled that he's a part of a team to first discover Z-space. I like engineers.
4. Marco cares a lot for him. He must be a great dad before the dead mom incident.
Ok, this really looks like I'm all over Marco that's why I like his dad... but yeah, it's true.