The big functional difference between the 28 and the 27 is variety.
You can find the 27s in six cataloged barrel lengths: 3.5", 4", 5", 6", 6.5" and 8.375" in nickel and blue. The model 28 is really only found in barrel lengths of 4" and 6" (there are a very very few 8.375" Model 28s that I have seen photos of - never one in person) and they are almost exclusively finished with a blue (there are a few that have been nickeled, but most of those are done after they left the factory).
Both are great guns. You cannot go wrong with either.
