It's not easy to state what EM's are the best or most collectible or even if an accurate A-list exist.

Bally, Williams and Gottlieb are most likely are at the top of the EM list of all the manufactures. It might be a good place to start since all three manufactures have so many great games to choose from and most of the time are separated by a fine line in game play etc.

Hopefully you have a serious EM collectors close by in driving distance from your location. There you could learn about EM's from conversation and playing their collection, forming your own opinions and taste on what you like about EM games. Also perhaps there might be some pinball shows close by that have some restored EM's to check out. If your close by to New Jersey you are welcome to play my EM collection.