For stickers you want a vector design, vinyl cutters don't take well raster images. Also if your design is printed, a vector will ensure the best print quality since it will be resolved on the printer instead of resized and sent as a raster.
Ok, I went too technical again. Stick to Adobe Illustrator or Corel DRAW that handle vector graphics. Photoshop, paint shop pro, mspaint.exe is no good because they work with bitmaps (or raster) unless you do a draft and vectorize it afterwards.
At least here, print houses like their digital material in cdr, emf, wmf or ai format.