QS is one of the best, if not the best early solid state games IMO. I used to collect early Ballys until I played QS, Nine Ball, Sea Witch, SG, Stars, etc. When I go from a good classic Stern to a Bally, I get bored real fast. Having said that, Stern also made some duds playwise like Viper, IM, etc.
The only one that comes close to QS is Dragonfist. I've only had mine for a few weeks, and it's like a combination of QS and SG. Still trying to determine which one gets the #1 spot.