I love both companies and own nib from both. My jjp games had nothing wrong out of the box other than having to adjust the shooter rod on hobbit. My Stern's were great to. Had to bend bracket on sparky, and had a dmd line go bad on Metallica. Overall both great experiences. Since then, zero issues other than adjusting a couple switches.
It seems like this post was spawned from a handful of jjp potc owners having issues. I can easily recall a lot more stern threads dealing with cabinets, ghosting inserts, node boards, etc..due to volume of games stern puts out.
Overall, both companies are releasing quality products. Jjp problems stem from the many mechs, and need small adjustments at times. Stern's issues are usually node boards, and cabinet/play field issues. Both in which seem taken care of upfront and never to be troublesome again in most cases.