I've owned the Surface Pro 3 for more than a year and a half - definitely one of the better PC's I've owned but has a few deractors. The first is noise - the fan is noisy and tends to whir up when doing almost any task - even watching videos online. The second is the temperature above the display - it often sits around 30 degrees celcius - hot enough to fell uncomfortable when using digital ink. Three is the limited RAM in the device - being stuck with the 4GB model was a bit of an issue when multitasking or even having multiple tabs open through web browsing. There were no major slow points thanks to the SSD, but performance was definitely affected by the total RAM.
I have owned the Lumia 950 XL for a year, and used it extensively over that year. At launch, there were many issues - the first being updates that rendered the phone inoperable for the first month. Now, the software is fast and fluid; not yet perfect however - occasionally, the phone restarts while using Windows Hello. Within the last 4 months, a few key improvements have been made - first is camera speed and quality, second is Windows Hello, and the third is the presence of syncing across a wide range of UWP apps