Hi there

It does come down to personal preference, space available, the look and feel that you are after and machine maintenance and I am sure other things that I may not have thought of.

So I did a quick few drawings (with a room measuring 4.3m x 2.8m with dimensions of the pinballs based on a CFTBL and a WW) to help explain some options, but personally my thoughts in relation to the drawings are:
I like to keep a 100mm off the walls so when you need to lift / move there is no risk of damage and the legs extend past the back of the machine also.
I like to have enough room to slide the glass out the front (shape represented in blue) allowing easier maintenance for globe changes etc without moving other machines.
I like to have enough room to remove a machine without moving other machines. (option 2 and 3 are better for this as option 3 is a little more of a juggle).
I have at least 100mm between machines to allow a little easier access for maintenance and also good if you have a few people around a machine watching, as there is enough room for a person either side to watch.

In the end if you have more machines you can get more in but it gets tighter to move around, and no this is not my place but purely just food for thought and a picture is equal to alot of words.

Hope it helps you.

Below is option 1, 2 and 3