For working at home I would like to go MAC if for no other reason then the bundled software that comes with it and being an IT guy by profession I would like to know how to run one.
That being said It is really hard for me to justify the extra cost of MAC, as you can download open source software for PC's that will replace any piece of software you can think of that you have to pay for(The GIMP is a great example of a photoshop replacement). It maybe a little different, but for the most part it will get you from point A to B just the stuff you pay for. You can get a hell of a PC for 700 bones.
Computers are tough to buy for me, because in a year there is always something way faster. If you go the PC route make sure you get the 64 bit OS, and as much memory as you can handle, 4GB is absolute minimum for me, I would prefer 8 GB or more.
Also don't pay for the Anti virus software, to me that shit is an absolute rip off. I have been running AVG free for the last 3 years, and Microsoft is offering a free Anti Virus software now as well.
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If your good at something, Never do it for free.