I have and use both a Contax IIa and a Leica IIIf. Both were overhauled by the best -Don Goldberg did the Leica and Henry Scherer did the the Contax. Both are superb cameras.

I mostly use the Contax with a CV 25mm lens when I'm using my Nikon SP with the the 35mm f/1.8 Nikkor lens. The Leica IIIf most often has the CV 21mm lens on it when my Leica M4-P has the CV 28mm Ultron f/1.9 on it.

Both have good 50mm lenses - the Canon 50mm f/1.8 and the Sonar f/1.5. I'll flip a coin to see which one I'll take when I want just one body and a 50mm (sometimes the M3 with the ZM 50mm Planar f/2 wins).

As for teles I have a 105mm Nikkor for the Contax. The Leica has a 135mm Canon that never gets used on it as the rare times I use the 135 it's on the M3.