Pinball is one of those things you need to discover on your own. Everyone has their own opinions. Personally I love system 11 because I played them in high school and that's what I love. I couldn't recommend whirlwind or earthshaker because you would find them simple and boring.
Get out and play a bunch. Find what really appeals to you. Never over looks a game because other people say it's not fun.
Last piece of advice, if you are a hands on type of person, after you start building a collection. Look into buying something on the low end and reconditioning it with your son. I have more fun working on games then playing them.