I have a 4 yard box pleated Cameron of Erracht in a medium weight that Matt Newsome made for me. I have never worn a kilt so comfortable or fit so nicely--albeit I'm gaining weight since marriage, but that has nothing to do with the kilt!
Four yard kilts are better balanced and I've never had any problem with the "swing"--but I'm a dancer so I get a little more swing than the average kiltie anyway.
I've recently read Bob Martin's booklet which discussed the matter--and I've been to the Scottish Tartans Museum in NC to see the 4 yard box-pleats dating back hundreds of years. So, it's not a matter of what's "right" but rather what's "right for you." I have come to prefer the look of box pleating as cleaner--showing off more of the material.
Beyond kilts that I might inherit, I will NEVER go back to knife-pleating. I will always purchase a 4 yard box pleat. (Besides, buying 2-4 yards LESS material will give your wallet a breather and you can afford other such niceties as kilt jackets, beautiful hose, etc.)