Well, PC itself is great for all of the above reasons enumerated in previous posts.
A few of those are:
1. Great webmaster/mistress(s/es). Seriously, Steve knows what he's doing. So does Jake, Andy, Audy, Jess and the rest of the admins.
2. Staff listens. While they may SEEM like a cliquey bunch (and they really aren't like that if you bother to try to understand them), they do try their hardest to listen to the wants and needs of the members. New blood is recruited into the staff on a regular basis. They even pay heed to cranky old members like me, when I'm not taking the cranky vet thing over the top. You don't have to be an admin or a mod to change things around here. You just have to be loud enough. :3
3. Welcoming. You can't find a more welcoming place on the internet. It's so well moderated, policed and integrated as a community that there's room for everyone, no matter how big or small your ego is. :P
4. Features. Many, many forums are excruciatingly miserly with features. PC isn't, and it goes above and beyond even the base forum software code to provide more enjoyment and entertainment to it's users.
5. Maturity. PC isn't just for kids. PC grows up with you, it evolves with you, it even accommodates adult discussion without losing it's "Kid-friendly" atmosphere these days. It is still haven to even the oldest of members, who may still have lives but can find time to visit. It's so wonderful that you WANT to make time for it, even as an adult.
6. Variety. PC isn't hidebound, nor does it require you to talk about only Pokemon. It accommodates a wide range of topics from a-z excluding explicit ones. That makes for a civilized discussion usually and works well.
In short, PC just works. It rivals Facebook without being Facebook. It is original, diverse and generally is like a huge mall, there isn't anything you CAN'T find in it. XD