good question. It depends on how many pins you have i guess.

I am lucky enough to have a heap of machines so i placed them in the following order.

1. All sega concave 1997 1998 models side by side.
2. 4 x star treks all next to each other (2 x next gen 2 x 25th anniversary)
3  i try to put all williams next to each other
4. i try to put all data east next to each other.
5. since i have 2 x gamesrooms, i put the ones i play the most in the closest gamesroom
5. when i am drunk, all the above goes out the window and i just watch all the flashing lights. lol