Both of which will be bigger, uglier, noisier, run a shitty OS with poor quality rip-offs of the Apple iApps package. The Mac will also be much faster than a £600 PC in real world use.
I don't know where you get the idea of £200 for a keyboard, mouse and monitor. I could get all that for a fair bit less, or just use the USB keyboard and mouse I have spare in the house along with my lovely Sony
15" CRT monitor.My Shuttle box cost about the same as the Mac Mini but isn't anywhere near as capable - as well as being (relatively speaking) a large ugly box. In short, it's a bargain.