A Magic Mouse seems redundant if you have a Macbook that has a gesture-controlled trackpad. Why would you use a mouse for gestures when you can use your trackpad.
There are some scenarios where I do prefer to use a 2 button mouse with click wheel. (playing video games, video editing, photoshop)
I would recommend a bluetooth mouse or a wireless with USB dongle (where the dongle is only a few cm thick). Sometimes bluetooth mice get "un-paired" and I have to re-connect it. And I always buy Logitech. Always.
Because, as two people have pointed out, if you use your macbook as a desktop at home (it's plugged into a screen and a keyboard), your macbook is closed and therefore the trackpad is not available to you