Since my car is black, I use a gas powered pressure washer with a foam cannon from Amazon ($18.00) I want as little swirl marks as possible.
My technique is pressure wash the grit and grime first, then foam cannon the soap on. I use about a half a cup of Meguiars car soap in the cannon with soft water right out of the softener. Well my foam is thick, it's about a half inch thick when it goes on, about like the foam in the Chemical Guys video. I just don't point the cannon so close as to blow the foam off of the car. Works great!!