There are times, when my four year old daughter will NOT do what we ask of her, no matter how we ask, what we reward (even bribe), what our arguments are, or how much we point out it is in her best interest. When I lose my temper (agreed, it's not a good thing) and pull out the Mad Dad voice, she changes her demeanor and does what I tell her to. I don't think that this is a better way to parent. I don't think it should be the first thing to rely on. I have seen the difference, and it is immediate. I _am_ working on improving so my temper doesn't get lost, but the question was which works MORE, as opposed to being ideally BETTER.
It is my opinion that children are more motivated by compassion and understanding than screaming and yelling. I feel that screaming at children is more likely to frighten them and cause trauma that would have the opposite effect of taking away their hope as opposed to motivating them to succeed.
I think that compassion is more important when it comes to motivating a kid. I do not think there is any benefit for a kid to have to deal with screaming whether it is from their parents or other people. I think a kid shouldn't be taughted principles due to fear but instead due to compassion.
Children are more motivated by compassion, rather than screaming, because children who are being screamed at cannot think. Positive reinforcement is the best motivator for a child. The child wants to hear that they did a good job. Controlling out of fear will work for a while, but ultimately compassion is better.
I think kids are much more motivated by compassion than they are anything else. The reason for this is because it makes them feel better. I am not saying you should be compassionate to a kid throwing a fit for no reason--this takes sternness--but overall, of course compassion is the better choice.