Originally Posted by presspass
I have both and use them interchangeably. The TTLs have had more recent CLAs than the classics so they are a bit quieter. The meter display is different. The classic has the two arrows; when both are lit, the meter says the exposure is correct. The TTL has two arrows and a center dot. When the dot is illuminated, the exposure is correct. It will also light the dot and either the underexposure or overexposure arrow; that indicates a half stop either over or under, so it is a bit more precise. In use, once you've become accustomed to the way the meter reads, there is no major difference. Both cameras will operate without batteries - only the meter fails to work - but the TTL will not fire any flash if the battery is exhausted. If for some reason you decide to use a Visoflex, only the III will work with the TTL - the body is just a bit taller than the 2, 3, 4, and 6. The Visoflex 11 will work with those models as well.
The TTL was also available with the .58, .72, and .85 viewfinders. The classic is typically a .72 viewfinder; there were .85 models made but they are rare and expensive.
Hope this helps.
This pretty much says it all. I prefer the metering display of the M6TTL over the classic. I like that center dot. However the ability of the eye and brain to set the exposure to perfectly balance the brightness of the two arrows on the M6 classic, is quite good! So the TTL's center dot doesn't really lead to more accurate exposures. The Classic is just as accurate.