As soon as Williams starts making pinball machines again we will grade them side by side with Stern, er, wait a minute.....
Let's not forget that Williams had their "cost reduction" periods as well. As a matter of fact, AFM was one such game. Doesn't seem to have hurt the resale value much.
Overall I have had pretty good luck with NIB Stern games. TRON was a bit of a nightmare, but the others have needed nothing more than a few tweaks here and there; nothing a few hours of work won't fix. A box opening party usually turns into a game fixing party which I find kind of funny, but so goes the hobby.