Since this has moved from what Parelli teaches to what is right, here is the book answer:
I think dressage teaches 0 deg (I'm not a dressage rider). The US Cavalry taught 45 deg out. IIRC, George Morris says 0-15 deg, but that some people may need to be up to 45 deg out on some horses. An early book by VS Littauer taught 30 deg.
My guess based on being a 50 year old with tight legs and hips when I started is that the best answer is either A) as far forward as a relaxed, draped leg allows, or B) whatever is taught for a specific sport.
I started at about 60 deg out. My right leg now normally is about 30 deg out, and my left is 45 or more
. That happens when I jog as well - my left foot hits the ground about 20 deg further out than my right. That may be some weird thing in my leg. Oh well. I have to ride with the body I have, and it sure ain't perfect!
I suspect Linda Parelli now teaches toes forward due to her involvement in dressage, while Pat Parelli will continue to ride however he does. Judging from a sample of pictures, that would be in the 15-45 deg out range.