The strength of the Sony mirrorless ecosystem is its wide range of lens choices. A system that locks you into their brand lenses is a poor value proposition.
Mid range zooms for Sony
At 470g, the Sigma 28-70/2.8 is considerably lighter than its 835g 24-70/2.8 sibling, and significantly smaller too. It might make a good choice for an all-arounder, and a 28-70mm still matches up great to a 12/14-24mm zoom and 70-200mm zoom, for those looking to do it all with just 3 lenses.
Please use these links to buy, thank you. See also Voigtlander for Leica M.