I was a child when I played my first EM, and they were more of a novelty for me. I played late 60's EMs in the early 70's and I grew up around 70's EMs and then found that I enjoyed the early Bally SS machines (as Dad operated countless Bally's around this time). Williams SS were no match, either were the hybrid EM/SS called SYSTEM1. Stern simply copied Bally, so their machines were a little "different", yet faster than Ballys. System80s were too ambitious, the technology could not keep up with the creativity of the GTB designers. As a result, they followed the fate of their predecessors. The early 80's Ballys were simply awesome. The artwork of these games is unmatched in any era. Fathom, Viking, Medusa, Paragon (1979) and Flash Gordon had the artwork AND the game to match. Bally "lost the plot" shorty after (BMX, Hardbody eww..), Williams found stability in their boardset and came up with some classics. Stern disappeared and although SYS80 were a bit of a flop, these games from the era 1980 - 1984 are highly desirable.
I love EMs and they bring back a flood of memories every time I play or restore a machine. A very special "soft spot" for Bally EMs.
Anything after 1985 is much the same. DMDs came along, and needed flashing lights, ramps and toys to attract players. I do enjoy playing DMDs, but they are really not part of my childhood, so they are not my favorite era. But I'm GLAD the industry kept progressing as I enjoyed Funhouse, Addams Family and CV.
Easy to work out my favorite era is 1977 - 1983
KISS, Paragon, Fathom, Viking, Flash Gordon, Meteor, Galaxy, Flight 2000, Freefall, Spirit, Haunted house and Black Knight