I decided to take my A7R out with its native 55mm lens; SEL55F18Z. This lens is possibly the E-mount's best lens in terms of measurable, objective, optical performance. It also exhibits rather pleasing (if a little bland) subjective qualities such as bokeh, colour, and contrast.
As with any system, there are certain perks in using a native-lens. For example, full exif info and lens corrections, fly-by-wire autofocus, and electronic aperture control. These conveniences are most welcoming when one's out and about, as fiddling with fully manual systems isn't always the most relaxing thing to be doing. Different horses for different courses.
The real pièce de résistance is the sheer resolution of this lens. The lens out-resolves the 36 MP full-frame A7R sensor, which is most evident on a pixel-by-pixel analysis of an image. However, it's also noticeable on an image when viewed as a whole. There are details in the details.
Those following my blog will know that though I am in possession of a couple of 50mm lenses, the focal length is relatively unfamiliar ground. As with anything, the only way to improve is to keep trying, make mistakes, and learn from them