Very thorough and realistic review (not just chart shooting). The Samyang is a nice surprize, in terms of IQ.
The Zeiss 135/2 is the first lens I have where the f/stops are there to control the DOF and nothing else. I have used it for concert shots (brassband) with great results despite the lighting: multiple spots, ever changing colors... and I fully agree with the observations made re resistance to flare.
And the handling... well, similarly, I was tempted to buy the Samyang 35/1.4 rather than the Zeiss 35/2, but the "dry friction" feel of the Samyang definitely put me off, although in terms of pure resolution, the Samyang may have been slighlty better. No regrets here again : later I became aware of the fantastic resistance to flare of the 35/2, my highest contrast lens for against-the-light shooting.
The 135/2 is the king of clarity. However for portraits I often prefer the old 105/2.5.
