Building your own PC has got to be the way to go..
1. You decide what goes in there so there's no rubbish in there and it is not unbalanced i.e. great processor with crap graphics card (if your into gaming) etc..
2. I'v always found building your own PC to be cheaper
I just put my computer together last week, its nice to build it ur own. Also this is my first time to do it and it was pretty simple. The best thing is that u select what to put in it, and specially selecting the case!
good luck