I'm gonna offer my 1.25829 pence in the form of a good old fashioned roundup.
Apple MacsIn the matt aluminium/white->yellow plastic corner, we have the Mac. By far the most common iteration of this is the MacBook: its earlier generations were made from white plastic which turns yellow if you use it with sweaty hands, and shiny patches appear on the mousepad (itself a good invention, but there is multitouch on some other trackpads and a proper right click); there is also an aluminium, thinner one with a bigger trackpad and.. oh wait, that's all it has to offer. The only size it comes in is 13.3", a bit big to carry with you everywhere in one hand but still a good size, but its little sister, the MacBook Air, is truly astounding, the thinnest laptop in the world (..oh no, look at MSI, and the
1 USB port (what the utter hell?)). Each of these runs on old hardware (9400M.. lol), stifling innovation. Also, it costs £80 to upgrade from 2gb to 4gb RAM and
£720 to upgrade from a 160gb HDD to a 256GB SSD.

There exists also the MacBrick Pro, which is slightly larger and runs on the same hardware as the top MacBook, unless you spend an extra £200 for a slightly newer CPU and graphics chip.
Then we move over to the desktop segment. First we'll look at the Mac Mini, a dainty little morsel of Apple. The base spec isn't quite as good as the base MacBook, but it is a lot smaller, and it doesn't have a screen (quite an important thing to have), so you either find a cheaper screen or spend £635 on a 24" Apple one

- that's about as much as the Gateway XHD3000 30" if you do the conversion. The Mac Pro is simply ridiculous - the flagship offering has no prospect of SSD (or OCZ z-drive?) and the best graphics availible is one RHD4870, oh, and an extra CD drive will set you back 80 squids. And finally, the iMac: this actually offers the best performance to pound ratio but £880 to upgrade from 2gb to 8gb of RAM? No SSDs in sight? On the lower end, the same graphics chip as the laptop? It's high end desktop prices for laptop performance.
Now I have covered the actual computers, I must mention a few things common to all of them: the mouse; the keyboard; the software. The mouse/keyboard are simply awful and totally unusable. I don't know about the Mac-fanboys/people-who-use-Macs among us, but I can tell you that when I press a button, I like to know I've pressed it, and if I don't think I have, I press it again. If I had to use a Mighty Mouse daily, using my computer would not be an 'enjoyable experience (like using a power tool is enjoyable)' but a constant annoyance. The keyboard also provides little feedback to those who have pressed on it, so it's like drumming your fingers on a table. I think Apple have put looks before usability here, and they always have: I remember a perfectly circular Apple mouse from an iMac running OS8 (which broke several times) and a keyboard which was the total opposite of today's and took a hammer stroke to press the keys (which, consequently, broke constantly).
Mac OS X Leopard is fine, and it's mostly a matter of taste as to who likes it. I can see how it is user friendly and it 'just works', but fewer games work on it and the Mac ports aren't as good - they certainly won't run as well as on a better PC. I'm also not keen on Expose, and the dock doesn't come close to Windows 7's taskbar.
Windows PCsIn the beige, black, silver, red, green, blue, acrylic, stainless steel, polished steel, painted steel, carbon-fiber, glass, wooden, shiny aluminium, matt aluminium, anodized aluminium, plain aluminium, powder coated, spray painted, whatever-the-hell-you-want-it-to-be-made-of corner is the Windows PC. PCs, I believe, truly allow people to express their individuality, and PCs prove that people are inventive. The Windows PC is more versatile than a Mac: with a Mac you are limited to one design, one set of hardware and one set of values; PCs, however, range from the boring Dell Optiplex workstations to the Asus Eee keyboard PC and the HP TouchSmart series.
It's impossible to round-up every 'PC' as there are so many to choose from. That doesn't mean it's nescesarily hard to choose what you want to buy - you may simply want an HP Pavillion desktop (nice and simple) or you may know you want a Sony Vaio media centre PC (incidently about the same size as a Mac Mini but with more slots and a TV tuner and a keyboard with touchpad and a slightly better pricetag for the performance). You may also want to build your own, in which case you have a vast selection of cases (Antec, Thermaltake, even bloody MountainMods), many motherboards with different numbers of different ports to suit your individual need and with room for expansion, different CPUs, different graphics cards and manufacturers of RAM (all priced in real world prices) (I have 2 sticks of OCZ 'Special Ops Camo' RAM in my desktop in camo colours with a neat heatsink

, not to mention cool things like sound cards and KillerNICs, as well as potential for case lighting and huge networks of water pipes to cool your graphics card. Granted, some of these possibilities cost more than a Mac (except my RAM), but aren't they cool (no pun intended)?
Overall, there are more applications (therefore more choice) for Windows and we have better hardware possibilities (and worse ones, but for cheaper - why spend more for something slightly better if you don't need it?) such as touch screens, so I go with PC for the choice.
I'm expecting a long post about how Macs are more secure than Windows, so hit me.