This question gets asked a lot, so you might be able to find more comments via searching. That being said, my cocktail cab has only 3 non-arcade buttons: Esc (escape), P (pause) and a button to power up my PC.
My upright has pause, escape and "5" (coin up for P1). These are on a temporary piece of wood that's screwed into my CP. When I ever finish my cab, I'll probably drop the coin button, or make it hidden somewhere.... In fact, I'll probably hide a pause, escape, power and coin button somewhere on the upright.
Both cabs have keyboards attached to them (or close by) so I can make other adjustments as necessary, but I really wanted to keep the admin buttons to a minimum.