Over the years there have been a number of variations to the 1911 in terms of sights, safeties, hammers, frames and slide serrations. One of the major changes was the addition of a "firing pin safety" in the 80 series Colts. That safety has been also used in a "similar" fashion in the latest series Kimbers and S&W's. A large number of people believe that the "safety" feature 0n the series 80 is unnecessary. Many remove it.
The series 70's did not have that "firing pin safety", but utilized a "fingered bushing" as opposed to a "solid bushing" in the earlier, and later, Colts. The fingers have a tendency to break if not properly fit. Many folks replace them.
The earlier Colts had neither of these features, although there are a few with a similar firing pin safety called the Schwartz safety.
In general terms, the distinction is between the ones with a "firing pin safety" and without such. Which is "better" has been, and will be, argued for years.
dclark