1944 with invincibility on.
I find that my kids LOVE playing on the arcade machines but the games are mostly too hard (they were meant to eat quarters after all). With practice they have gotten good at a few (and by good I mean they can clear a level or two) - Dig Dug, Circus Charlie (trampolines), Ms. Pac-Man, Galaga '88, TMNT (after putting in like $10) and Ladybug to name a few...