I have an HP laptop. I've had it for about 10 months and it's working amazingly. Even when it stopped working last week, it repaired itself! (Only error it's ever had.) I was surprised. I was so scared that I would have to go to get it fixed, like with another one of my laptops which I couldn't fix myself. But I didn't.
I have the HP Pavillion dv6000. They probably have better models out now, but I love this laptop! It even has a remote control and now their laptops come in an environmentally friendly laptop carrier instead of cardboard and styrofoam packaging
I'm not sure about Dells, but we had those at school and they weren't anything special. They had errors a few time too.
I say neither, get a Toshiba. I'm on my second one and I swear by them. I've had Toshibas for six years, and I've had to have a repair exactly once. They're also among the most reasonably priced brands, especially at Best Buy. Dell has terrible customer service and Sony is ridiculously overpriced. I have no direct experience with HP, but I know they merged with Compaq and Compaq was terrible.
My sister, however, got so many viruses on hers that the entire system had to be wiped clean. She has no trouble on it now, but it was such a hassle trying to heal it before we made the "fuckit" decision. So, that being the only laptop I've personally owned, I say Toshiba is a good brand.