The difference between a regular optical mouse and a laser mouse is the light used to track movement. A regular optical mouse uses an LED light in the optical engine, while a laser mouse uses a laser to track movement. The more dots per inch (dpi) a mouse can track, the more sensitive and accurate it is. A typical optical mouse tracks between 400dpi and 800dpi, while laser mice track more than 2,000dpi.
Neither is really better; it all depends on your needs and preferences. Unless you're a gamer or a graphic artist with a need for precise movement, you'll probably find a 2,000dpi laser mouse too sensitive. Many gaming mice, however, allow you to switch sensitivity levels so that you have precision when you need it but can revert to 400dpi or 800dpi for regular mousing.
Besides their tracking speeds, laser mice work on nearly every surface, whereas optical mice may experience trouble tracking on black or shiny surfaces.