When I have held a pinball competition, the easiest n most simple way I did it was to give everyone  60 minutes practice on the 4 machines total between all machines I chose for the comp.

Then, it was play 4 games maximum per game, keeping your best 2 x scores.

The highest score got say 10 points. 2nd Highest score got 5 points. 3rd Highest score got 2 points.

At the end of the night, the person who had accumulated the most points won the trophys and so on for 1st, 2nd and 3rd places.
I found if I did it this way, consistency won the competition. You could get the 2nd highest score on each of the machines for exampole, and still win the comp.

An easy fun way to have a home tournament on older 90's dmd machines.