Hello,
Here is what I found from a user who owns both:
Dell
Pros:
No moving parts. Completely silent. (silence is gold);
Generally faster. (not that much, but you can feel it.)
Longer battery life. (4 cell, 4 Hours)
tiny AC adapter. (that's a big plus.)
Cons:
A little bit narrower than HP, but thicker. (1.3 inch vs. 1.0 inch)
Smaller screen. (9 inch vs. 10 inch)
Weird keyboard. weird key locations like these: ' ` [] \ / keys. a huge downer if you do coding.
HP:
Pros:
looks sexy. Great form factor. 1 inch thin.
10 inch screen.
perfect keyboard. (for a netbook. this is the main driving factor for me to purchase the HP mini in addition to my dell 9).
Cons:
Noisy.
Slower. (I have the 4200rpm HD version, but I heard the SD version is not any better.)
3 Cell battery, less than 3 hour battery life.
Very awkward Power adapter.
The center of weight is toward the hinge with scree, so easy to topple even on a flat surface.
No standard VGA ( a huge minus.)
more expensive (by like $50. but now they dropped the price 1 weeks after I bought it.