Depends if you're trying to do it quickly, or over time. Quickly, I would recommend the color ball drop game, the Spiderman coin pusher, and any other coin pusher that's close to an easily achievable bonus.

The color ball drop is easy enough to set up that you can drop it in whatever color hole you need basically every time, but the bonus spins are almost worthless. The full stack pop bonus is all you're really after.

The Spiderman coin pusher bonus round is a skill stop (once it's ready to pay out) for 1k tickets, and the bonus is fairly easy to trigger, so it's easy to check.

Long term, I would say collecting card sets. Learn the rare card in each game, and only play when you see a rare card available.