As someone who has had both devices, I ended up with the Nokia Lumia 2520. The wireless 4G/LTE connectivity, excellent screen, short charging times (coupled with long battery life) and portability of the tablet were all important aspects that helped my decision.
The Lumia is easier to hold around and comfortable because of the rounded edges VS. the sharp angles of the surface. Also because the screen is not too big, it is manageable to hold in portrait mode and much more comfortable. The soft touch of the device (black) is a bonus so it is pleasing to the touch. I also enjoy the super-fast charging (0-80% in one hour) so I can enjoy the tablet more on the go instead of being plugged in all the time, and I can get away with not charging. The power keyboard adds two USB ports, touchpad, physical keys along with an additional battery to supplement the main battery. It is also designed like a portfolio so it wraps and protects the tablet. I know the Surface will be offering a power keyboard with the battery priced at $199, with the Nokia Power Keyboard priced at $149.The lack of a physical USB port on the Lumia is not a drawback, you can find a OTG adapter for $3-5 if you look around.
Both screens are good, however the Nokia screen simply is unmatched by any tablet on the market for having the best color accuracy, brightest display, Nokia Clearblack to reduce reflection, and outdoor visibility. It is 74 percent brighter than the Surface 2 and 52 percent brighter than the iPad Air. You can read the view on DisplayMate, a site known for performing intense testing on displays.
Windows Tablet Display Technology Shoot-Out
The only drawback I
had is that the screen has no oleophobic coating, so it is a fingerprint/smudge magnet. I solved this issue buying the IllumiShield oleophobic screen protector on Amazon, and it has all the properly cutouts and significantly reduces smudges and fingerprints so it is smooth to operate the screen. I know the Surface has an oleophobic coating on it. The Surface also has the kickstand, and since I had the Surface before, the removal of such stand in the Lumia took a little time to get used to, but eventually I got over it.
Both are great devices, it just depends on how you think you will be using it. The ruggedness of the Lumia 2520 allows me to take it anywhere, indoors and outdoors, without having to worry about if it will scratch or break. Hope this was helpful and assisted you in your decision. Good luck!