The M6-ttl has three LED indicators for exposure: < o >. Unlike the M6 Classic, you move the aperture and shutter dials in the direction of the pointers to get the correct exposure, which is when only the central "o" is illuminated. This is very convenient. (Yes, there's also the lightning bolt LED that comes on when using a flash.)
The M6 Classic has only two indicators (pointers) for exposure: < and >. You know you have the correct exposure when both red triangles are illuminated. The shutter speed knob rotates the oposite way to the M6-ttl, so you can't use the pointers as a guide as to which way to turn the shutter speed dial to get the correct exposure.
I chose the M6-ttl over the M6 Classic because of the more intuitive relationship between the viewfinder indicators and the aperture/shutter dials.
Incidentally, The M7 costs a lot more than either the M6 Classic or the M6-ttl, but you do get Aperture Priority Automatic Metering, which is nice. For me the downside to buying an M7 over an M6 was that the M7 relies on batteries to work. If the M7 batteries die on you, you only have 1/125 and 1/60 seconds shutter speeds. On an M6 (Classic or ttl), all the shutter speeds would still work as only the meter requires battery power. In fact, you don't even need a battery to shoot with the M6 series of camera.
Go for the M6-ttl, or the M6 Classic if you find one at a very good price. The money you save on not buying an M7 (or M8 or M9!) could go toward buying a Leica lens. The Summicron 50 and 35 are both very nice lenses to have.
P.S. If you wear glasses, you should probably go for a 0.58 viewfinder.
Last edited by Obtong; 07-26-2010 at 10:17 PM. Click to view previous post history.