I don't follow either trainer. I can totally agree with some of those who have seen a lot of horses ruined by PP methods. I've seen 'em too.
I find that CA is often the more popular and respected trainer, of these two. Parelli is often "dissed" for being too soft, too emotion based, too "woo-woo".
Clinton Anderson is looked up to being a tough, no nonsense guy, which is more admirable in our culture. However, I agree with Wanstrom and GallopingGuitarist in that CA is overly aggressive, has very little real feel for a horse and often creates an unhappy horse who obeys unhappily.