Quoted from too-many-pins:

I think the mistake people make is thinking one machine would be great but I only want to own one and I want to keep it for years is regardless of what machine you pick it will get old over time. If you have "X" number of dollars you want to spend on pinball and have the space I would spend that "X" number of dollars on 3 machines instead of just one.
When you have one machine it will basically never get played after a few months but if you have 3 in the same room they will get used all the time. Reason is fairly simple - you turn on the machine and start playing it and all of a sudden you wife or son decide that looks like fun, they sit and wait for you to finish playing and after a few minutes they get distracted by something else and they are gone. Now you get done playing and no one else is wanting to play.
With two or three machines (same thing happens as above) - other person or people turn one one of the other machines and start playing. Next thing you know one of you gets board with the machine you are playing and you move to the third machine. All of a sudden two hours have passed.
In a perfect world one machine isn't your best choice and if you have space I would pick having two or three System 11 or data east machines over having one more expensive machine. Maybe it is just me but one machine just will not have the stay power two or three would.