I used to have an older model of the Linksys posted above, with only wireless B, and it would not reach more than about 30 feet from the point where it was positioned. Its wireless was almost unusable except for the room right next to it (a guest room). We luckily had our house wired with Ethernet so it was not a big deal most of the time, and it was a major plus on how many ports it had. Now, our new house has only a few ethernet ports, mostly in the basement for DirecTV, Xbox 360, etc., so I knew we needed a better wireless router. After a good deal of research, it was between the Airport Extreme and a Linksys router that is no longer in production. We currently have all our computers hooked up over a wireless network--the Macs are connected via wireless N and get great speeds and the PC and iPod Touch are connected via G and I can use my touch in the backyard. We use all the Airport's ethernet ports, but it is not a big deal because it is connected to a modem with multiple ports. I could not get one of my older printers to work via USB, but it was due for replacement anyway, and so I purchased an Ethernet printer to share over the network. I have also tested the AirDisk. If you have a Mac, it works almost seamlessly, although it is a bit slow--much slower than a USB connection, let alone FireWire. The AirPort utility is also very well made--it works seamlessly on a Mac (not so well on a Windows XP machine) and will automatically alert you of new updates.
So it depends on what you need/can use. If you want a router with good wireless capability, I recommend the AirPort. If Ethernet is important to you, the Linksys might be the better route, although if you really want the features of the AirPort, you could always get an ethernet splitter for the AirPort. I like the extra features the Airport provides-printing, AirDisk, good wireless range, great interoperability with other Apple products, the ability to add more Apple routers and set them up as extensions of your network (I am actually contemplating putting an AirPort Express in the basement so we can get a better reception down there), and the user-friendliness of the AirPort utility (it is very easy to set up and change settings if you know a small amount about what the settings do). The Linksys uses a web interface, which I find a bit annoying. My old Linksys also had problems with dropping out, even over ethernet.
Hope that helps a bit!