It depends on what you are looking for as they serve different purposes. This comparison is not with the Leica lens in your question but it could give you some idea.
I had both Zeiss 100mm f2 and Leica 100mm APO macro. Zeiss is very sharp, contrasty, and very 3D. It's one of the sharpest lens I have used. That said, I sold it and kept Leica because Zeiss CA problem is a lot more frequent than I expect. And I really like Leica color rendition over Zeiss. And Leica is also quite sharp too.
I was looking at a c/y makro planar. I think one of the reasons, in the back of my mind, why I was put off by it was the CA I was reading about. My lens I am selling to make room for a new lens does this. It disgusts me.
I love my 35 Cron. I think it is one of my most favorite lenses I have ever had. The crazy thing is, I have always enjoyed longer lenses but this lens just opened my eyes.
Can't help you on the Zeiss side, but the Leica 100 APO macro is breathtaking. I have had mine for about 18 months, and can't say enough nice things about the sharpness meshed with the dreamy bokeh (even at smaller apertures).
I also like it for non-macro uses, though it is best there for stationary scenes. While I like the look of the images that I have taken of my kids with it, getting them to hold still while I rack the focus is a lost cause. That enormous focus range (something like 8 revolutions from 1:2 out to infinity) leads to tremendous precision. I picked up a nice Nikon 105/2.5 for a light weight portrait alt.
The makro planar looks to be a great lens too. I see myself getting one in the next couple years, not as a replacement for the Leica but to achieve different looks in the images.
For a cheaper alternative, the Leica 60mm macro is also fantastic and quite compact for what it is. They run a fraction of the price and are incredibly sharp. I have been toying with unloading my 50 cron and replacing it with a 60 macro.
Well, I just got back from FedEx... I dropped of my 85L II. This was my second time around in that relationship. When I got back, I grabbed the camera, and a dose of medicine to help me stomach the parting of ways.
In my case, all the medicine I needed was my 35 Cron. I took about 5 shots. Done. Enough.
Now I am just waiting on 80-90 focal length in the R mount.
The 90 APO? The cheapest I've seen that gem go for lately (June 2010) is $2300. Rare bird.
Though recently an 80 went for $1500 at KEH. Hard to match the 85/1.2 though. I doubt you would do better with the Leica R 80.
Canon 85mm 1.2L is hard to beat but it's different from Leica 80mm. For portraits, I much prefer 80mm as the color tone just glows at f2.8 or wider. Zeiss 85mm 1.2 Anniversary is better than Canon 85mm 1.2L at open aperture.
This is with Leitz 350mm @ f5.6 on Canon 1Dsm3, handheld.
Shore bird of Santa Monica Bay, shot about a month ago. These birds work the surf zone for sand crabs.
