Hard to know what to recommend ... what is it you want? A collection that is fun to play (for you? for casual and beginning players? for sake of nostalgia?)? Fun to look at? Fitting a theme? Expected to make money from people in public?
I'm a big fan of System 11s, and I would be more than happy with a collection of just 12 of those and the left-over 80K. Similar systems, parts, wouldn't be a maintenance nightmare, etc.
BK2K
Diner
Dr. Dude
Earthshaker
Elvira ATPM
Grand Lizard
Mousin Around
Pin Bot
Radical
Swords of Fury
Transporter: The Rescue
Whirlwind
In a dream world, I'd probably diversify by manufacturer and time period, and not considering maintenance headaches and parts sourcing. This is a crude example, but
1-2 EMs
2-3 early SS games
2-3 System 11s
2-3 WPCs
2-3 current companies
and then rotate stuff out as it got boring to me.
Interesting thought experiment!