My EMs? Always set to 5 balls.

My early Bally solid states? (Mystic, Flash Gordon, Fireball II) 5 ball.

Anything later than that? 3 ball.

It's how the games were meant to be played IMHO, and the rules and gameplay are the most balanced because of it. And the old games are drain monsters. So even a 4 player game on Flash Gordon with 5 balls can be shorter than the first ball on Metallica. It's nice, because you can all hang around the game and play together, and it rotates fast. A couple minute ball is a great ball usually. Keeps it moving. And you're bound to have an unfair shit ball or two, these games are like that!

For me System 11/DMD games are just too long on 5 ball. I keep extra balls on instead, set to 3 ball. Make you earn another chance, and feel like you accomplished something by earning it. You might play 5 balls, but only if you're playing well and on a run. And that's fun to me.