For me, the deciding factor was size and weight, along with the ability to just use it as a Tablet. I looked at the Zenbook, the Dell XPS 13, HP Spectre x360, Lenovo Lacie Z, Venue 11 Pro, along with the Surface Pro 3, and the Surface 3 met my needs better than all the others. If size/weight are not significant factors, and if you didn't need a Tablet, or want to use it as one, then the Asus or other choices might be better options.
I got the bundle at Costco for $699 for the 4gb Surface 3, Pen, and Keyboard. I added a Gigabyte Bluetooth Mouse for when I use the S3 as a Laptop. At 10.52" x 7.36", and 1.37 pounds without the keyboard, it functions extremely well as a Tablet. The integral kickstand is just awesome for this. I'll use it for casual websurfing, read books via Kindle, highlighting text with the Pen, texting with the Verizon Message+ App, etc.
For more serious Laptop use, I have Photoshop CS6 on it, and with the Mouse and keyboard, it functions quite well. Not a serious workhorse, but gets the job done.
I also added an additional 128gb of Storage with a Sandisk Ultra MicroSD card. When doing Photography travel trips, a small Transcend USB 3.0 CF Card reader transfers files incredibly fast, the USB port will support my Seagate 500gb External Hard Drive Backup, etc. Gives me the same basic capabilities as a much larger/heavier laptop, at a fraction of the size.
So as others have pointed out, you need to figure out what details and functions are the most important to you, how you're going to use the device, and then pick the one that matches your needs, and your budget, the best.