A really hard question so many good ones. For me I'll stick with ones I own or have owned in the past.
EM- Solar City a great drop target EM.
SS- Flash I love the sounds a bit of everything and not that hard or expensive to obtain a nice one.
So many other great machines out there the problem I find with asking other peoples advice is that as with everything (and maybe even more so in the pinball world) one mans trash is another mans treasure so you really need to play them for yourself if you get the chance.
My favorite era is SS because that is the main era of pinball from childhood so really it's all sentimental but if I was to be 100% honest I would have to say that no EM or SS gets the blood pumping like a good game on a good DMD.
I'm trying to build a small mixed collection of keepers from each era..best of both worlds.
