I haven't had much time to keep up with hardware lately, so I won't suggest one over the other. It's always going to depend on which model from what company you compare. Both Dell and HP are large companies and both make a decent product.
You want to watch out for the advice that tells you to blindly go with whatever companies without providing any reason. I would suggest you look out for a computer or two that interests you, then read many reviews. It's better this way, getting advice from those that have used them. It's also best to read several reviews. Some reviewers can be biased.
Now my experience with hp laptops the past couple of years hasn't been the greatest. They make a nice laptop, but they tend to run pretty (extremely) hot. My experience is limited to only two higher end models though. I replaced my last fried HP (GPU went bad) with a higher end Sony Vaio and I've been really enjoying.