It boils down to the kind of artwork you're preparing and what you intend to do with it. Vector vs. Bitmap Vector graphics are made up of shapes defined by mathematical expressions. Each pixel has a specific location and color value assigned to it. Bitmap graphics can represent subtle gradations of shade and color. A disadvantage of bitmaps is that they represent a fixed number of pixels, so they can appear jagged and lose detail if they are rescaled or displayed onscreen at a higher resolution.
Vector art consists of scalable shapes.
Bitmap art contains individual pixels. Vectors also produce more compact files than bitmaps, so they're quicker to open or download on systems with limited memory or low-bandwidth connections. Bitmap images can represent rich and subtle gradations of shade and color, so they're appropriate for artwork created in painting programs and for continuous-tone images such as photographs. You might also want to convert vectors to bitmaps to apply distortion filters or other special effects to them. Both Illustrator and Photoshop can rasterize your vectors into bitmaps.