The body holds film and lens and opens and closes the lgiht hitting the film. The lens determines the quality of the negative/transparency provided the film is flat, the shutter accurate and the lens mount parellel to the film; most bodies, even the lower end do a decent job in doing their job. Many lenses are good but more important in the process than the body in delivering the quality.
I am not promoting either Leica or Zeiss glass. Both companies have had good to excellent. Look for the glass that you appreciate and like and then make a decision. Remember if on a budget, there is also the Leica CL that can use the Leica and Zeiss M mount and is 1st rate as a user body at a bargain price compared to an equiv. M body. I use the CL and after 20 years would not upgrade to a M body in lieu of buying a lens to use with it. Also, the is the Minolta CLE that is where Leica probably would have gone if it continued development of the CL.