There are numerous Dell machines that offer way beyond the performance of a Mac Mini and for less money; XPS 8700 is one that offers a quad core processor that is a whole generation faster than the Mini and with a significantly better graphics card for less than the cost of Mini.
Granted they are not as small as a Mac Mini but it's a desktop not a portable.
Again, argue that you prefer the Mac operating system or how it looks but trying to claim a Mac Mini offers better performance for the same money as a Dell is just wrong.
This was what drove me off the Mac platform, after a decade. I like OS X, I really do, but the price/performance tradeoff is immense, and the residuals in Mac kit aren't what they were.
I had a choice: spend £2K+ getting an iMac with a meh processor and a meh graphics card (because the top-end options are very meh; the iMac is made of laptop components), or spend £800 at PC Specialist getting a box with room for more RAM, two graphics cards, and 7 internal drive bays. No, it doesn't look as nice and I had to buy a separate screen. But I can live with that.
I also found the two iMacs I had (a white one, and then an aluminium one) to be very unreliable. Both lost their GPUs to thermal failure, both had to have optical drives replaced. The Aluminium one also had its display replaced. AppleCare is an absolute
must on these, because unless you're an extremely competent and confident hardware tech, they are simply not user-serviceable. Also, a new display panel for a 27" iMac is £600. Oof.
Not to mention that all of these repairs required a trip to the nearest authorised Apple service centre, which in my case was Jennings (York/Scarborough, very professional, if you are in the NE and need a Mac, these chaps are first-rate). In my PC, I would simply get the part bought on overnight delivery and have it fitted within ten minutes of getting the parcel.
I would have liked a Mac in the old Mac Pro tower format, but without the ruinously expensive Xeon processors, which offer little benefit to desktop users.
OP: I echo the advice given here - base your choice of hardware platform on your software preference. If you like OS X, then buy a Mac, but if you're content with Windows, you will get more value for money with a PC, which will be uglier.