Hi Louis,
A fair comparison could be made between the Makro-Planar 100mm 2.8 C-Y mount and Makro-Sonnar 100mm 2.8 N-mount.Both lens have very good reputation.I owned the Planar one and it does provide me with unbeatable image quality and colour rendition.Zeiss also provide excellent data for comparison.
From the MTF diagrams,the Planar performs slightly better than the Sonnar at non-makro setting.At 1:10,Planar marginally performs better particularly when u=20mm.At 1:1, 2.8 the two lens are more or less the same but Sonnar performs better at u=20 saggital R=40c/mm.Sonnar is brighter at the periphery than the Planar and perhaps this is why it has the name Sonnar.The Planar has marginally less distortion.
In conclusion,both are very good.If you wish to have marginally clearer pictures,choose the Planar.If you wish to have brighter margins,choose the Sonnar.
Another fair comparison can be made when f=5.6 between C-Y Planar 85mm 1.4 and G Sonnar 90mm 2.8,Planar in this produce better image quality and less affected by distortion.This time Sonnar does not appear to be brighter.
Perhaps the most important thing is to enjoy pocessing the lens,all of them are very good.Joseph