You cannot go wrong with a classic square-style sticker. The clean, crisp edges and simple-but-elegant look make this the most straightforward and popular option.
Actual Sticker Sizes (Width & Height) 2x2 - 1.86 x 1.86 3x3 - 2.77 x 2.77 4x4 - 3.71 x 3.71 5x5 - 5.55 x 5.55