I love my SP4. I've compared it to the Pro side by side and ended up settling with an iPad Air 2. I regularly use the Surface Pen, and it came with the Pen.
What sold me the most is the full Windows OS on board rather than an iOS. If the Pro came with OSX I'd have been sold. The SP4 also has a USB port and expandable memory, and you can't beat that Type case. Facial recognition, fingerprint ID on the Type keyboard, so dang quick to turn on its mind blowing. And I prefer Cortana to Siri.