It really depends on ones individual needs. One person's usage might definitely gravitate toward the yoga so its hard to say if one is better than the other, even though one might clearly have better specs than the other.
The surface pro is for those who want more of a TABLET experience. Some advantages include:
-Has pen input
-Seems more appropriate to use at various occasions whether formal or casual
-A lot more handy, and you won't have exposed keyboard keys when holding it as you would when the Yoga is in tablet mode
-Sharper screen at 1920x1080 squished on a 10.6" screen VS. a 1600x900 on an even bigger 13" screen
The yoga 13 is for someone who wants a more LAPTOP like experience. Some advantages include:
-Can be used a lot more effectively in the lap
-Has more ports
-Has an adjustable angle screen
-Has a real keyboard
For my use and wants, I got the surface pro because I use it often like a tablet, but it can be my computer when I need it to be which is also often. If a person doesn't need tablet functionality so much, then I would simply advise they don't get the surface and stick more to a traditional laptop like the yoga 13, because it least you'll get some sort of tablet functionality, even if it is quite poor as a tablet. Some people buy a laptop and buy a separate tablet like an ipad but I don't want to carry around 2 devices as I am often on the go and need everything in one place.