I agree - probably five to start, and learn the game, but if you want to know where you stand against everyone, it's all done on 3 ball (for modern games, that is).
EMs, definitely 5 ball. I can play longer on one ball on a DMD than some five ball EMs.
I volunteered at playland not at the beach yesterday, giving out tickets for the pinball games. They have a score sheet on each game and if you get a certain score you earn tickets which can be redeemed for prizes.
Some guy asked me what the trick was to getting a lot of tickets so I told him to play hokus pokus, which was on 3 ball. You only need 30000 to start earning tickets. He was averaging 60000, so he was earning 5 or 10 tickets per game, and since the games are really short, he earned a lot of tickets.