I'd go with Home Build.
I chose this because of several reasons:
1. A Dell would cost about £300 more than building it yourself
2. No, you don't get tech support, but if you've got TechIMO, who needs tech support now?
3. You can upgrade your system without just buying a new computer, you can take components out of your case and fit new ones in, like a new mother board for example.
4. You can overclock your system, with a Dell, you couldn't.
5. When i build computers, it gives me satisfaction in knowing i have achieved something not a lot of people know how to do, or haven't done.