With wireless N still only being a draft 'standard', you need to get all of your N kit from one vendor to be 100% certain of full compatibility and performance. Since the N cards in Macs are made by Apple, the AP Extreme is the only choice. Having said that, if you only want to share internet and small files between your machines, or you have one or more machines with g or b wireless cards then any router will suffice for your needs.
Personally, I like Netgear routers for their extra features (My old one had better wireless range than my current Airport basestation (UFO Extreme). I gather that linux based Linksys boxes are nice and hackable though.....