If you're not afraid of digging in and learning some basic maintenance, there's nothing wrong with an EM. Especially when dealing with projects, you don't need to worry about things like boards being bad, etc. Ems are only slow if they're badly maintained or set up that way; they can play just as fast as a solid state.

SS is going to vary a lot of manufacturer/system. Williams or gottlieb system 1 you might want to avoid, unless they have repro mpus, in which case there's no real issue. In general, with ss games the boards are the single biggest source of issues, and the biggest possible money Sink to repair/replace, so do a bit of learning about any given system/board set when considering purchasing one. Know what's in the game currently, what replacements are available, how much they could cost, etc