I really don’t think any particular era or generation of games is easier or harder to work on. They all require the same level of soldering and electronics prowess to diagnose certain issues.
What does differ between generations/manufacturers/eras is the level of support they get from other collectors.
Ask a tech question for an 80s or 90s Bally or Williams game and you’ll get a ton of helpful responses.
Ask a similar tech question for an 80s or 90s Gottlieb game, and you’d be lucky to get a couple good responses.
It’s not that the Gottlieb game is harder to work on, they’re just not as popular, we’re manufactured in lower quantities, and therefore don’t have a huge army of fans to support them.
However, parts availability seems to be very good for basically any game these days. You can’t go wrong. Very little is unobtainable.
My suggestion is to get a game that you WANT to work on. Something worth your time and something that’ll keep you motivated when you find yourself in a pickle—regardless of era or manufacturer.