from personal experience hp's are more reliable than dells, i have used 2 hps and 2 dells. My current hp is used as my primary computer, i edit all my pictures on it, i carry it wherever i go. My first laptop was an Hp, i used it for 3 years, without any real issues other than the battery dying after a year and a half and then the cd drive went out after almost 3 years. The essential parts functioned properly until i gave it away as a gift. then i got a dell, i had problems with my hard drive crashing twice within the first year, i figured i had a lemon so i replaced it after 11 months, the second dell wasnt much better, the fan stopped functioning properly, i ended up having to get the motherboard replaced, i had to replace the hard drive 3 times within a year and a half also (i only had to pay for one of the harddrives everything else was under warranty).
I will say that dell has great service when you are under warranty, but when you get out of warranty thats when the real cost comes in.
If you are getting a dell definitely go for their business line, they are way more reliable thats why they cost much more. but i would recommend hp any day all day.