HP's battery can make Dell's bite dust.
Regarding display, HP was on par till pavillion series, not anymore. In fact, it's among worst now (G6 series).
HP also fked it's good speaker. But build quality has definitely over the time.
Regarding service, Dell can throw HP out of window. Though I had very good ASS exp with HP, but that still is not found at majority of the places.
If you are in a dilemma to choose between both, go for Dell now.
Sujay has summarised it beautifully.
Here's a short comparo
1.Battery-The new MU-06 battery(launched in Jan2012) is a pretty strong battery and is branded as a long life battery. Heck even HP gives a warranty of 3 yrs on it when purchased new. Even I can vouch for it-My 2 yr old battery still gives a 4 hrs of reading time with GPU switched off and in power saving mode.
My Mantra which is also proven to extract maxm battery life-Use battery as low as possible.Remember its Lithium ion tech which has a fixed number of charge-discharge cycle.Earlier Nickel Cadmium Battery has to be operated on battery power once in a while..Not any longer.Even if u use on Battery,make sure no HEAVY draining tasks are carried out,like Game or a 1080p video on GPU. If rate of discharge is too high,th lithium ions fail to get charged again,and it shows as wear. This comes from my experience,and all my friends who follow this rule dont have to replace battery too often.
Dell definitely has weaker battery than HP. So in battery round HP wins.
2.HP doesn't have a good speaker now. DTS is simply crap in front of Dell. Dell wins hands down.
3.Build quality has greatly improved...Earlier G series of HP were of iffy quality,not any more.HP is now as good as dell in terms of Build. Only area where dell is still superior is the consistency. SO Dell wins,but by a very negligible margin.
4.Screen-HP wins in 720p easily,but its not great...Its just that in 720p screens,Hp is better than Dell.Best display is Sony.
5
.Service-Here's what most people dont know-Both HP and Dell use REFURBISHED parts for replacement in their Service.But i've felt,that the quality of refurbished parts in dell is not up to the mark...My friends have repeatedly faced motherboard and HDD failures on their XPS. Even though service of Dell is quite prompt,it lacks depth.For complex issues,they surrender much quickly than HP.But again its nitpicking. Where HP really triumphs is that they give 3 yrs free warranty,where as dell charges some 12-18k for it.
My pick would be HP
Also Processor in Dell is ULV which is quite a bottleneck in performance.