HP and Dell both make laptops which are very specifically targeted towards mainstream laptop buyers, but the way they go about doing this is actually quite different.
Dell tends to create designs which are simple, but can be spiced up with a splash of color if your choose (and are willing to pay around $30 or $40 dollars more, as the special color options available with Dells are an extra cost). Dell products don't stand out overly much, but when examined closely they do provide very solid build quality for the price. The keyboards are some of the best in the business, although they do show a little flex. The trackpads are simple, but functional. Displays are pretty much par for the course, with poor viewing angles but good brightness.
HP designs usually don't have as much color, but instead make themselves stand out by adding patterns and textures to the lids and interiors of the laptops. The degree to which you'll like this is going to be determined by personal tastes - I prefer Dell's simplicity, but your opinion may differ. The same goes for the keyboards and trackpads. HP has been experimenting with keyboards and trackpads quite a bit and has many different styles available. I generally find the keyboards lacking in feel and the experimental trackpads - such as those which have no visual indicator of where the trackpad begins or ends - do not earn much praise in my eyes. However, HP does make good use of multi-media keys in their multi-media laptops.
Overall, Dell has a slight advantage in this area, mainly because of the keyboards and trackpads. Overall build quality is very similar between the two laptop brands.