My recommendation depends on your budget. If you can swing it, the Sony 16-35mm f/2.8 GM II is the best of the best for the Sony system. Unbeatable image quality and that bright f/2.8 aperture across the zoom range. Obviously it commands a premium price though. For a more affordable option that still performs great, check out the Sigma 14-24mm f/2.8 DG DN Art lens. Third party but impeccable optics at a lower cost than Sony's GM lens.

Let me know if you need any other details to make your decision! Wide angle zooms offer so much creative potential.

The new announced Sony FE 16-25mm f/2.8 G lens is a compact choice for a7CR.

Of course the Sony 16-35mm f 2.8 gm ii

if you are looking for a cheaper options, get the Sigma 14-24mm f/2.8 DG DN Art Lens.