Y. Dobon , Jul 27, 2000; 06:20 p.m.
Contax/Carl Zeiss's official stance is that AE and MM lenses are identical in optical performance; the only difference is in diaphragm action. The decision is really up to you. I don't use shutter priority nor program AE exposure modes on my 167MT, so I personally wouldn't hesitate to buy AE lenses.
That said, I have not done any side-by-side AE vs. MM lens comparisons. Lens testing is not one of my photographic interests. I've used both types and they all seem to take very nice pictures. Good luck with your purchase decision.