The arduino itself is cheaper (30$), but it depends on what you want to do. If you want a stand-alone 3 channel PWM RGB ambient light that runs by itself your personal pattern on some power leds (1A or more/channel), using direct input (some switches, a temp sensor, a touch sensor, RGB input) Arduino is easier and cheaper, and delivers 256 steps of brightness per channel. If you want to drive many lights up to 500mA/channel, use basic preprogrammed patterns, and don't mind the computer being on all the time, the LED wiz is a good choice.