Build your own, it can save you a lot (from what I heard). It might not look as shmexy, but it'll still work as lightning if you build your own.
A lot of people say "Build my own computer? That's WAY to complicated". Not really, just do some research, buy the pre-made parts and put your new computer together. If you like to build things, not only will you be saving money but you might even enjoy constructing one.
Do NOT rely on 'PC MEAL' computers from eBay, no matter what their ratings are and how cheap they are compared to their specs (just looks here:
http://forums.whirlpool.net.au/archive/1776519 ). I personally do not buy custom-built computers from online shops because they usually require you to buy the default Windows software with it as well in a bundle (not that it's expensive), so you need to combine shipping, which I just don't like because things can go wrong etc.