I bought the PET book. After advice from here.

I think a course would be better.

I think with all of them, you will only take out what you are prepared to do, you know, what actually already fits with your parenting ideals. I didn't write that well. I guess what I mean is each of them would provide you with some good helpful advice / techniques. You aren't going to totally rewrite the way you parent, just gain some insight into what works sometimes and why.