Quoted from Det_Deckard:Correction to my comment or my serious answer.
The best size is one that doesn't annoy you with maintenance. To me, there is no greater nightmare than a huge collection that keeps falling apart. I like fixing stuff but when you take on projects and don't have a lot of time, it eats at you when you realize that pinball xyz has literally been down or a few switches haven't been replaced for months.
Well said, agreed