If you are creating white decals I assume you are using white decal paper???
Most laser printers will make good decals. I have never used a Brother brand laser so can't speak on it. What are you using to create the graphics?? A vector type software like CorelDraw is needed to create good art. Bitmap like paint or word will not produce good decals no matter the printer. All these are my own decals printed on a good laser.....
A little more info and maybe I can help......been making decals since I was 9 years old!!