I had three copies here last year just by coincidence of some trades I'd made. Since they were on hand, I tested them for sharpness and out of focus quality, plus spent some time just shooting with the Sonnar version.
I've had the 1st Gauss version for some time, but seldom shot with it since it is not a focal length I use much. I only realized a couple years ago what a great lens this is. A Sonnar version showed up with some stuff from a friend, then a mint AI version showed up with some other stuff.
The bottom line is that they are all great. Each newer version showed some improvement in sharpness, though all were really good. The sharpness difference between the two Gauss versions was just barely distinguishable to me with a much more precise setup than I would ever use in real life.
I was already familiar with the character of my Gauss lens, so spent some time shooting with the Sonnar. In the end I kept the one I already had (early Gauss) and sold the Sonnar and AI on. I already had a friend interested in the AI, and sort of prefer the single coated look anyway. I didn't find any advantage to the Sonnar; it had a very nice look, but so do the redesigned ones. I have seen one claim that the very earliest Sonnars were the sharpest of all at infinity; I have no reason to doubt or to believe that, but the Gauss is so sharp it challenged my ability to test it. I suppose somebody might prefer one or the other for portraits, but I can't imagine being dissatisfied with any of them.
Now, it would be great if I just had some use for it. I will say that this was a very handy focal length back when I had newspaper jobs.