How do I chose a good budget desktop computer?

I have done some maintenance over the years but will admit that I haven't been the most regular with it.

When I upgraded from windows vista to windows 7 a couple years ago I wiped the hard drive clean and started over with a fresh install. Other than that I have maybe defragmented the hd two or three times at the most since then. There are some programs that I should uninstall as well. Since I probably will keep this device as a backup I will be sure to take your advice and try to keep my next system from getting to this point in the first place.