I just got an XPS 15 yesterday with the 16gb/512ssd and granted im not using it for work, just personal use, I love the 4k display. I thought I might as well get it so it can be more future proof. The ram can me upgraded to 32gb and well the 512ssd is pcie and is plenty fast. Touchpad is the best I ever had. I never tried macs though.
When I tried it, I thought it was good, but I'd tried a mac touchpad an hour or 2 earlier and I think it's a bit better. The Dell can do more things (e.g. hand over pad blanks the screen), but as I recall, some of the scrolling gestures were iffy. In fairness, the machine I was messing with didn't even have gestures turned on until I did it, so it's possible some drivers were missing.
That said, the Dell clearly has a better screen and CPU. If I bought one today, it'd be the XPS or Precision 15.