The worst Contax has to be the AX. Whoever thought of a motorised telescoping body to deliver slow and hesitant autofocus should have been shot.
The second worst Contax (to me) is probably the 167MT. It worked well enough but I found the handling bizarre. Contax got it so right with the Aria, which I think shows that Kyocera/Yashica did learn from their mistakes.
I was a big fan of the N1. It performed and handled superbly. If only the N Digital had not been such a disaster, I think Contax would still be with us.
I didn't make the N Digital my choice for worst Contax ever because I admired the sheer bravery of Kyocera/Yashica in developing that camera when they did. The problem was entirely with the sensor, which was so bad that Pentax did not even release the DSLR they had developed around it.