I wouldn't restrict yourself to just a Gottlieb.. each manufacturer had its upside and downside and none of them made a perfectly simple system to maintain. Each plays differently.. WMS will be fast.. Gottlieb feel very slow in comparison, Bally games are kind of in the middle. But when it comes to repair etc.. each have their own difficulties

Agreed. Don't restrict yourself to one manufacturer. As mentioned, keep away from Playmatic, Recel and Euroflip. Zaccaria's are rare - but hard to find parts. From a restoration point of view, Gottlieb have more parts available. Williams are good players, but I much prefer Bally's. No real reason other than they are often overshadowed by Gottliebs. From a maintenance point of view, single player wedgeheads are the easiest. From a player's point of view there are tons of great games that won't break your wallet ;

Spirit of 76
Target Alpha
Dealer's Choice
Alladin's Castle

Wedgeads ;

Sky Jump
King Pin
El dorado

Just do your homework and ask a lot of questions