I like playing them all. Each genre,manufacturer,solid state boardset,display type,EM,sound system,ect. each had their unique challenges and solutions from a pinball designer perspective. I like seeing both the great (as well as the not-so-great) solutions that different companies came up with to make a game that was marketable to the general pinball playing audience.
Having said all that, my favorite era of games is 1975 to 1985 since most "market changing" advances in pinball history were made during that time period (EM --> SS design). I mean DMD and stereo sound are great and all but they really don't have the heart-and-soul factor like a great playfield design or shot layout does.
One other thing to mention is that if it was not for "video games taking over" arcades in the 80's, pinball would have probably have never been so eager to push the limits of what a solid state pinball could do in 1980 with things like multiball,stereo sound, or even later alpha-numeric and dot matrix displays.
I love the pinball designs they came up in this time period. One reason my favorite designer is John Trudeau is that the concepts he brought to his games like Spirit, Hollywood Heat, Judge Dredd and CFTBL were so well done with the technology and budget he had to work. None of his games are "the best ever" so to speak but I really think his execution is among the best and most "out of the box" insight that any designer ever had with the possible exception of Mr. Ritchie.