The Dell is cheaper. The Dell is more expandable/upgradable. It is smaller and lighter. I presume it has better battery life vs. the HP's 3 cell battery. The Dell has a standard VGA connector. The Dell's SSD
's probably perform better than the HP's 4,200 rpm drive (not sure how the performance of the SSD
's would compare). You can buy the Dell in black or white, while the HP is only available in black.
The HP has a better keyboard. You can buy either an 8.9 or 10.2 inch model. The 10.2 inch keyboard will be more usable. You can get the HP with either an SSD
drive, or a 120GB 4,200 rpm drive. You'll be able to replace the HP's drive with a Toshiba 5,400 rpm bigger driver if you want.
Personally, if you want a 10.2" netbook, I'd buy the Samsung NC10. It has a faster hard disk, a matte display, the best keyboard, the best battery life (a 6 cell that doesn't stick out), bluetooth included rather than extra, and is available in a cool blue color.