From a Nikon shooter’s standpoint, the only reason I would switch over would be because of the 135/2L. It’s quite good.
That being said, I get along pretty well with the Zeiss 100/2 Makro-Planar.
My go to lens is the new Sigma 35/1.4 and I can’t live without the Zeiss Distagon T* 2,8/21mm ZF.2. I’m a landscape shooter though, so there’s that to account for. For portrait work, I’d have to say I generally grab the Nikon 85/1.4G or the Zeiss 100/2 Makro-Planar.