Vaser liposelection is another form of liposuction. As such, its contouring effect is mostly due to taking out tissue. It can enhance your buttock by taking tissue away from its surroundings so it "shows" better. This result can be achieved by both traditional or Vaser liposuction.
The Brazilian Butt Lift starts out by removing fat to countour the butt, but the fat removal process has to be done very carefully to preserve the fat cells. The fat cells are then injected into the butt to give it increased projection and a more rounded shape.
If your goal is to change your body proportions to enhance the butt you already have, liposuction (traditional or Vaser) will do just fine.
If your goal is to increase volume and projection of your buttocks, The Brazilian Butt Lift is what you want.
In the past, many women chose the first option, but changing taste is leading many more women nowadays to choose the latter. I love doing the Brazilian Butt Lift, so I'm very happy more women are choosing it.