I find all the back and forth here laughable. It's silly that people would get so emotional over products that do pretty much the same thing, and barring unforseen technical problems will both perform equally well in the task at hand. Obviously nothing is equal and that both sides have benefits and negatives, but I think if your dealing with < 4 hard disks they will both get you to the same place. > 5 discs and drive extender has the edge for versitility (raid can't use firewire/usb for expansion, at least as far as I know). Otherwise, just use whatever makes you confortable.
For myself, I prefer WHS because my backup is in the 4-5 TB range with duplication, and I still need room to grow...and also because I like my backup to be easymode. I would prefer a nice expensive hardware raid option with Risc and lovely raid certified hot swap harddrives in a nice server tower, with spare drives on standby..but hey I can dream

. In my view, the linux options are just as viable, sometimes more viable, albeit and little more hands on to setup. In some ways they are superior to WHS, but like I said earlier on....choose the right tool for the job you want done.