I have had 5 Airport Extreme's and 2 Express's and I would say go for the Express. The new ones comes with N enabled and you could hook up a hard drive using the USB in the future. For an apartment, the express is more than enough to cover it unless you have VERY thick walls.

Also, with the express you have the ability to play music to external speakers in your house controlling it from your Macbook or iPhone which is useful.

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2011 ///X5 M (On Order)

2009 X5 4.8 M Sport Space Gray/Black Fully Loaded

2007 GMC Yukon XL Denali Loaded and Customised