I will start out saying I am biased, I bought a Dell. It is an excellent unit no matter the price. Like any computer unit, some have problems. Like any computer unit, the vast majority are perfect. As I have told many people, it is not if I have trouble with a computer but when you have trouble with a computer who is standing behind it. I would think you can't go wrong with either Dell or HP. The question comes down to how much do you want built into the unit and how much are you willing to do with addons? Builtins add to the possiblity of problems with the unit. The more complexity the greater the likely hood of a problem. On the reverse, the more addons the more you have to cart around with you.
I dont' think you need to worry about the ruggedness of Dell. I have read several posts of people dropping them and they keep on working. One guy dropped it from about 6 feet onto concrete. Also there are some very rugged cases available for both units.
In my book, the most important aspect is value. For the price of the HP, you can buy all the addons you need plus major amounts of memory for the Dell which would put it over the top in my book

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Good luck in your quest.