If you ask about good 80-200's these two will frequently receive honorable mention. I'm told the Leica is even better, but I'm not ready to get into Leica territory. The Nikon f/4.5 square back is also a good lens I shot years ago, but decided against tracking a copy down to include as I've largely moved away from Nikon.
So let's get right too it!
Wait, first a note... When testing I usually put the camera on a tripod, as I've done here (if note I'll mention it). I then manually focus using 11x magnification or whatever it is on camera. I'll focus wide open then stop down without refocusing while I shoot. If a lens exhibits focus shift it'll be penalized accordingly. Sadly I'm not perfect. As the 135mm test below shows, it appears that the Contax is back focused and the Canon is correct or slightly front focused. No, I'm not re-doing it. I have a full time job, shoot part time for hire and have a family. I'm not sure how I even manage to get this done once... But I'm honest so I'll call it like I see it. Okay, that's out of the way, now let's get right too it!
First, a couple across the board observations... The Canon is a thicker lens, the Contax is a longer lens. The differences aren't huge but they're there. Weight between the two is fairly similar and handling of both is good. I didn't bother to take shots of the lenses, like most old tele-zooms they're long and thin. Two other important distinctions I noticed while shooting these lenses, one negative for both. The Canon does not handle flare well. At All. So if you're shooting towards the sun, forget about it. The Contax seems much better, but I haven't stress tested it the way I did (incidentally) the Canon. For the Contax, as the shots below show, it generally trails the Canon in global contrast. Easily enough fixed these days, but it was pretty apparent. So onto the crops.
In the centers I see more CA and smearing at f/4 on the Contax. Mind you, neither is bad, but the Canon is better to my eye. The story continues at all apertures. The Canon has a slight lead. I'd actually chalk this up to slightly better micro contrast of the Canon, allowing for better differentiation of the grasses and roof shingles. If they weren't side by side though, I couldn't guess which was which.
In the midframes things change and the Contax pulls ahead. I see cleaner detail at all apertures in the Contax, though I think you could also say the Canon maintains slightly better micro contrast than the Contax.
In the corners, it looks like the Contax has a hint more vignette than the Canon but I'm picking. The sharpness situation seems to have again flipflopped, with the Contax slightly ahead, a lead it seems to maintain. Again they are very, very close.
If you shoot 80mm a lot, pick one and be happy. I'm pretty sure that's going to be my conclusion throughout though...
In the center the Canon is winning, handily. It has me wondering if I had a focusing error here with the Contax, but I'm not trying to take anything away from the Canon! The Canon showed cleaner detail wide open at 80mm as well, so I think it might just be a sharper f/4. Things get better at 5.6 for the Contax and it's close by f/8 but wide open is significant.
Midframes, okay I'm getting some confirmation from these shots. The Canon is more front focused, the Contax is more back focused. Look at the grasses and tree branches here and the sharpness flipflops. I think sharpness is closer than these crops indicate but I'm not redoing it, so take what you will from this...
Corners look like a push between these two at 135, but we know things are iffy here. Regardless I see better contrast again from the Canon. Neither is poor either. So let' stick with:
If you shoot 135mm, pick one and be happy.
In the centers, the Canon is the better lens wide open. It's a good deal sharper and it carries more contrast. At f/5.6 the Contax makes strides but still doesn't catch up to the Canon. By f/8 they are pretty close. The Contax doesn't win but it's about the same.
The trend of the other focal lengths continues, the Contax has better mid frame results at all apertures. The Canon catches up at f/8 but never passes the Contax.
Likewise in the corners, the Contax doesn't look much worse than it's center, while the Canon struggles a bit wide open. I don't believe this to be a focus issue either. Both the trees behind as well as the sliver of grass in front look better in the Contax example. To me, this is the biggest performance difference of these shots.
You can probably guess, just pick one and be happy! The trend is fairly consistent (if we just ignore the 135mm focal length) the Canon is sharper in the center, the Contax is sharper in the midframe and edges. The Canon carries more contrast if you're shooting SOOC JPEGs and don't want to mess with editing or changing your JPEG setting. Otherwise the contrast difference is well within editing tolerances. So it's worth considering how you'll use this lens here. If you're trying to isolate a central subject than the Canon's sharp centers may be important. I do like these lenses at 200mm and close focus, it throws the background into a nice fuzzy blur. But this is also not a lens traditionally used for portraiture etc. And so if you're using it for landscapes or similar, the across the frame performance of the Contax, particularly in the corners is likely of interest. Still, neither shows enough deficiency to say there is a clear winner. So enjoy some comparison images below, then pick one and be happy.