A Wired one can be extremely annoying since the ports are on the left and you are most likely to use the mouse with your right hand, a Wireless one can be a bit of a pain if the USB Dongle is long, so I would get a Bluetooth one, that said I didn't really find a lot of choices
The Magic Mouse is cute and works nice, but it's not good for pro uses or gaming, not a big improvement over a Trackpad, if you have the money get the Logitech MX Performance Mouse, It's a great piece of hardware, the USB Dongle is short, You can charge it with a wire and still use it and the buttons fit very well for OSX Common features like Exposé, Spaces and Dashboard