One advantage of the NX200 is the controls. These things are often a matter of taste, but most people agree that the Samsung way of doing things is much nicer and more intuitive than Sony's.
Another big advantage to Samsung is the lenses. If you're after a mirrorless camera that's truly portable, Samsung's range of lenses is particularly appealing, and includes a nice selection of very high quality pancake prime lenses (with more planned on the roadmap). Sony's lenses look rather bulky and/or poor quality by comparison.
In fact, the only real advantage I can think of for the NEX range is the price, at least until you get up to the rather lovely top of the range NEX-7, which adds a few features missing from the NX200 (built-in EVF, built-in flash). But then it is considerably more expensive.