Basically, both will come with same memory (8GB) and same disk space (1,5TB). At the moment, most important difference to me is processor: intel i7 870 versus intel i5 750. I have been reseraching in the internet, and I cant see many differences between them, except for price (not relevant when buying prebuilt system as I am doing).
Difference in price is about 100 euros (Dell is cheaper)
My main purposes for this new computer, among usual home use (browsing, downloading, watching media...) will be to work with huge photography files
On cybermonday I got the HP i7-860 version of the HP...same box/MB/512mb of video (same card)/6gb Ram...it runs very quiet, very cool, and works well with photoshop and Canon's photo software...this 870 is a bit better all around and so I can recommend it.
I'd recommend it over the Dell....but get an additional HD...most would say get a 64gb SSD for the OS...and use the 1.5TB drive for data/photo files...if not an SSD, at least a 7200 rpm HDD (with 16mb cache) for that purpose.