I've still got a 139 and an AX. I also used to have an RTS which I sold, as for me it didn't do much more than the 139.
I too have been looking to the future, particularly as my AX developed a bizarre fault on a recent trip. I've got 4 Zeiss lenses, and 4 Tokina C/Y fit lenses, so have also been considering the 5D. If I eventually get get one, I'll probably regard that as the worst Contax.