I have owned the Contax 139 and a couple 167 MT's. I have handled the RTSll, Aria and also various Nikon bodies. To me the Contax cameras were much more ergonomic than the Nikons. Of course this is a personal preference. As far as durability both Contax and Nikon were great. A fellow I knew at the local pro shop told me that the biggest problem with any brand of 35mm cameras was the manual film advances jamming. The 167 MT solved this with built in motor advance.
You can't beat Zeiss lenses but of course Nikkors are not bad either.