Raid: I have not done a side to side comparison, my sense is that the strengths are distributed slightly different ways. For instance, the 45 mm G-Planar was so good that I actually bought a G2 in order to be able to use it. When the 50 mm Planar came out in M-mount, I ran out and bought one hoping it would have the same magic. It's a great lens, very sharp, and in many ways comparable to the 50 Summicron, but for whatever reason it didn't touch me the same way that the 45 mm lens did. Having said that, my current favorite lenses are Zeiss M-mount lenses. These include the 21 mm Biogon, the 35 mm/f:2.8 C-Biogon and the 50/1.5 Sonanr. Just can't say enough about these lenses. The one way in which they are similar to the G-mount lenses is in their color rendition. As for the G-mount lenses, I loved the 45 but merely liked the 35 and 90. I chalk this up to personal taste, as the images from these lenses were technically excellent but missing a certain something that makes you go, "wow, images from this lens are always just so special." Other lenses that have that quality for me recently have been the Konica Hexar AR 57/1.2, the Nikon 105/2 DC, the Sigma 50/1.4 and the 21 and 35 Biogons I mentioned above.
Edit: I am in the no-wobble camp.