My personal favorite is Dennis Reis. He's got his own horsemanship that is somewhere between Parelli and Anderson. I enjoy that he only has 1 course to sell and not about 100 different ones like everyone else so you don't have to buy a bunch of stuff. However, I do like Parelli and Anderson and I use a lot of their techniques. John Lyons also is good.
However, I do not like Craig Cameron. He is too rough-and-tumble for me and I prefer a gentler approach, but that's just me. I respect Stacy Westfall, but after seing one of her seminars I don't agree with all of her methods, and yet again, I prefer a gentler approach.
That's just my two cents though. I would recommend buying Parelli's book Natural Horse-man-ship though, it has lots of useful information with out all the showboating and high prices.
The art of horsemanship through sharing new ideas with one another