My daughter has the most beautiful eyebrows of anyone I have ever seen, and they are natural. They are arched. Little brown angel wings on an angel of a woman.
I keep mine their natural shape which has a little bit of an arch. I make them a bit thinner than natural (mine are dark even though my hair is light - completely natural) and clean up the strays but I don't really play around with the shape.
I trim mine, but I can't tweeze them because I got bit by a dog when I was about 8 and he went for my nose and left terrible scars that my eyebrows cover.