Probably the biggest single difference among these is the meter display. The EM/FG/FG20/FM variants(except the FM3a) use LEDs; the FE/FE2 use a match needle display. With the exception of the late model FM3a, all sold strongly which means no shortages on the used market. I often see the remarkably capable FG+50/1.8E kit in very nice shape for peanuts. If it matters, the EM/FG/FG20 bodies are a bit smaller than the FM/FE variants.