"DS: What is your favorite XPS model and why?"

XPS730X.  Intel 1st gen i7.  X58 chipset.  not my pc

best full tower case made by Dell ever.  3.5 mm thick Aluminum.  Brushed Aluminum or anodized paint job.  ATX motherboard compatible and upgradable.  Psu upgradable.  Automated fan and liquid pump cooling curve.  X-view clear side panel. 

Considering only the last 3 I've had (have had more though), XPS8500, 8700, and 8940, I'd have to say the 8500.

Based solely on reliability and upgrade ability . For some reason, it was easier in that XPS? Also, it just worked. Had enough slots for extra drives with cables for it and no need to be extensions or cables. Never had a heat issue. Easily handled 2 extra internal hard drives, and replacing the shipped one with an SSD. When the video card failed, a new one that was a large increase in power demand, and operational aspects just worked. Matter of fact, it is still in use. Upgrades had extended its life and even compared to my 8940, my wife doesn't see much difference in terms of operation. Doesn't even want a new one. There is an existing problem on the XPS8500 in that the drive LED doesn't work... not worth fixed, but other than that, it just works.

My 8700 is still operational, but it was starting to fail, slow boot ups and it appeared to be a hard drive issue, and I needed more power for a game anyway.

I'd say the XPS8940, but unfortunately I have an Nvidia card and suffer from lock ups randomly. One of the reasons is due to that my wife has no inkling to upgrading, even though the problem doesn't exist in the 8950. By the way, the way Dell responded to the XPS8940 Nvidia problem has caused MANY to make the same statement, "last PC I'd buy from Dell". When it works, it is my favorite... but when it lock up, no way, one of the worst PC's I've even had, and I've had PC's (and worked with or on them since the '70's), and that included the Radio Shack TRS-80!