Design and Quality
HP and Dell both are mass-market brands. They're not luxury companies, so neither brand has computers that are comparable to the best available from high-end brands like Apple and Sony. However, both HP and Dell have unique design languages.
Dell's desktop computers tend to be simple, but not nessicarily easy to ignore. The most basic Dell desktop PCs in the Inspiron line are usually clad in simple black cases, bringing memories of the days when Dell made nothing buy unexciting gray boxes. However, Dell's XPS line contains a number of beautiful PCs like the Studio XPS 9100, which features a slick silver, black and red-trim exterior. You'll also find a handful of speciality products from Dell, like the Zino HD and the Inspiron One all-in-one PC.
The basic computers from HP are not much different from Dell's; in fact, I'd say they're a bit more boring overall. However, HP offers some of the best all-in-one and touchscreen computers in the entire industry. If you're looking for something different from an normal desktop tower, HP is likely to be be the better choice.
Winner: HP. Dell and HP offer comparable traditional desktops, but HP's all-in-one computers are the envy of the industry.